CONFIG: update c++ standard, some compiler rules (partially addresses #2209)

- migrate to c++14 for most compilers *except* gcc.
  There are still many systems in use with gcc-4.8.5, which does not
  support c++14.

- initial rules for nvidia compilers (pgi is will soon be defunct).
  Not fully tested...

CONFIG: provide fallback value for the user directory name

- in containers may have an unset USER env variable.
  Default to 'user' to prevent ugly looking directory names.

wmake/rules/General/Clang/c++

@@ -1,6 +1,7 @@
+#------------------------------------------------------------------------------
 SUFFIXES += .C .cc .cpp .cxx
 
-CC          = clang++ -std=c++11
+CC          = clang++ -std=c++14
 
 c++ARCH     =
 c++DBUG     =

wmake/rules/General/Gcc/c++

@@ -1,3 +1,9 @@
+#------------------------------------------------------------------------------
+# C++14 support with gcc-5 and later, but several systems (as of 2021)
+# are still using gcc-4.8.4 (centos7, suse SLES12, ...)
+#
+# NOTE if your system gcc is new enough can simply use c++14 too.
+#------------------------------------------------------------------------------
 SUFFIXES += .C .cc .cpp .cxx
 
 CC          = g++ -std=c++11

wmake/rules/General/Icc/c++

@@ -1,6 +1,9 @@
+#------------------------------------------------------------------------------
+# Intel compiler is new enough to support c++14
+#------------------------------------------------------------------------------
 SUFFIXES += .C .cc .cpp .cxx
 
-CC          = icpc -std=c++11
+CC          = icpc -std=c++14
 
 c++ARCH     =
 c++DBUG     =

wmake/rules/General/Icx/c++

@@ -1,6 +1,9 @@
+#------------------------------------------------------------------------------
+# Intel compiler is new enough to support c++14
+#------------------------------------------------------------------------------
 SUFFIXES += .C .cc .cpp .cxx
 
-CC          = icpx -std=c++11
+CC          = icpx -std=c++14
 
 c++ARCH     =
 c++DBUG     =

wmake/rules/General/Nvidia/c

@@ -0,0 +1,13 @@
+#------------------------------------------------------------------------------
+# Nvidia compilers
+#------------------------------------------------------------------------------
+SUFFIXES += .c
+
+cc          = nvc
+
+cARCH       =
+cDBUG       =
+cOPT        = -O2
+cWARN       = $(FOAM_EXTRA_CFLAGS)
+
+#------------------------------------------------------------------------------

wmake/rules/General/Nvidia/c++

@@ -0,0 +1,37 @@
+#------------------------------------------------------------------------------
+# Nvidia compilers
+#------------------------------------------------------------------------------
+SUFFIXES += .C .cc .cpp .cxx
+
+CC          = nvc++ -std=c++14
+
+c++ARCH     =
+c++DBUG     =
+c++OPT      = -O2
+ptFLAGS     = -DNoRepository
+
+# - Standard warnings
+# - Less restrictive warnings (may be needed for flex++, CGAL, etc.)
+
+c++WARN     = \
+    -Wall -Wextra \
+    --diag_suppress=111,128,177,185,612,998,1098 \
+    --display_error_number \
+    $(FOAM_EXTRA_CXXFLAGS)
+
+c++LESSWARN =
+
+# Warnings
+# --------
+# Run with --display_error_number to get numbers
+# and --diag_suppress=XXX to suppress
+#
+#111-D: statement is unreachable
+#128-D: loop is not reachable
+#177-D: function was declared but never referenced
+#185-D: dynamic initialization in unreachable code
+#612-D: overloaded virtual function ... is only partially overridden
+#998-D: function XX is hidden by YY -- virtual function override intended?
+#1098-D: unknown attribute "fallthrough"
+#
+#------------------------------------------------------------------------------

wmake/rules/General/Nvidia/link-c

@@ -0,0 +1,5 @@
+LINK_LIBS   = $(cDBUG)
+
+LINKLIBSO   = $(cc) $(cARCH) -shared
+
+LINKEXE     = $(cc) $(cARCH) -Xlinker --add-needed -Xlinker -z -Xlinker nodefs

wmake/rules/General/Nvidia/link-c++

@@ -0,0 +1,8 @@
+LINK_LIBS   = $(c++DBUG)
+
+LINKLIBSO   = $(CC) $(c++FLAGS) -shared \
+    $(FOAM_EXTRA_LDFLAGS)
+
+LINKEXE     = $(CC) $(c++FLAGS) \
+    -Xlinker --add-needed \
+    $(FOAM_EXTRA_LDFLAGS)

wmake/rules/General/Nvidia/openmp

@@ -0,0 +1,5 @@
+# Flags for compiling/linking openmp
+# The USE_OMP is for OpenFOAM-specific use (general use is _OPENMP)
+
+COMP_OPENMP = -DUSE_OMP -fopenmp
+LINK_OPENMP = -lnvomp

wmake/rules/General/Pgi/c++

@@ -1,3 +1,6 @@
+#------------------------------------------------------------------------------
+# PGI Compilers are defunct - now in NVIDIA HPC SDK  (2021)
+#------------------------------------------------------------------------------
 SUFFIXES += .C .cc .cpp .cxx
 
 CC          = pgc++ -std=c++11

wmake/rules/linux64Cray/c++

@@ -1,7 +1,10 @@
+#------------------------------------------------------------------------------
 # Cray compiler - a gcc variant/wrapper
+# presumably new enough to support c++14
+#------------------------------------------------------------------------------
 include $(GENERAL_RULES)/Gcc/c++
 
-CC          = CC -std=c++11
+CC          = CC -std=c++14
 
 c++ARCH     = -m64 -pthread
 
@@ -15,3 +18,5 @@ cctoo       = $(Ctoo)
 cpptoo      = $(Ctoo)
 
 include $(GENERAL_RULES)/Gcc/link-c++
+
+#------------------------------------------------------------------------------

wmake/rules/linux64Mingw/c++

@@ -1,9 +1,12 @@
+#------------------------------------------------------------------------------
+# mingw is gcc, but new enough to support c++14
+#------------------------------------------------------------------------------
 include $(GENERAL_RULES)/Gcc/c++
 
 c++ARCH     = -m64 -pthread
 
-# With gnu++11 (not c++11) to ensure __STRICT_ANSI__ is not defined
-CC          = x86_64-w64-mingw32-g++ -std=gnu++11
+# With gnu++14 (not c++14) to ensure __STRICT_ANSI__ is not defined
+CC          = x86_64-w64-mingw32-g++ -std=gnu++14
 
 include $(RULES)/c++$(WM_COMPILE_OPTION)
 
@@ -34,3 +37,5 @@ LINKEXE     = $(CC) $(c++FLAGS) \
     -Wl,--strip-all \
     -Wl,--force-exe-suffix \
     $(FOAM_EXTRA_LDFLAGS)
+
+#------------------------------------------------------------------------------

wmake/rules/linux64Nvidia/c

@@ -0,0 +1,12 @@
+include $(GENERAL_RULES)/Nvidia/c
+
+cARCH       = -m64
+
+# Compile option is non-mandatory, but must be non-empty
+sinclude $(DEFAULT_RULES)/c$(WM_COMPILE_OPTION)
+
+cFLAGS      = $(cARCH) $(GFLAGS) $(cWARN) $(cOPT) $(cDBUG) $(LIB_HEADER_DIRS) -fPIC
+
+ctoo        = $(WM_SCHEDULER) $(cc) $(cFLAGS) -c $< -o $@
+
+include $(GENERAL_RULES)/Nvidia/link-c

wmake/rules/linux64Nvidia/c++

@@ -0,0 +1,14 @@
+include $(GENERAL_RULES)/Nvidia/c++
+
+c++ARCH     = -m64
+
+include $(DEFAULT_RULES)/c++$(WM_COMPILE_OPTION)
+
+c++FLAGS    = $(c++ARCH) $(GFLAGS) $(c++WARN) $(c++OPT) $(c++DBUG) $(ptFLAGS) $(LIB_HEADER_DIRS) -fPIC
+
+Ctoo        = $(WM_SCHEDULER) $(CC) $(c++FLAGS) -c $< -o $@
+cxxtoo      = $(Ctoo)
+cctoo       = $(Ctoo)
+cpptoo      = $(Ctoo)
+
+include $(GENERAL_RULES)/Nvidia/link-c++

wmake/rules/linux64Nvidia/c++Debug

@@ -0,0 +1,2 @@
+c++DBUG     = -g -DFULLDEBUG
+c++OPT      = -O0

wmake/rules/linux64Nvidia/c++Opt

@@ -0,0 +1,2 @@
+c++DBUG     =
+c++OPT      = -O3

wmake/rules/linux64Nvidia/c++Prof

@@ -0,0 +1,2 @@
+c++DBUG    = -pg
+c++OPT     = -O2

wmake/rules/linux64Nvidia/cDebug

@@ -0,0 +1,2 @@
+cDBUG       = -g -DFULLDEBUG
+cOPT        = -O0

wmake/rules/linux64Nvidia/cOpt

@@ -0,0 +1,2 @@
+cDBUG       =
+cOPT        = -O3

wmake/rules/linux64Nvidia/cProf

@@ -0,0 +1,2 @@
+cDBUG       = -pg
+cOPT        = -O2

wmake/rules/linux64Nvidia/general

@@ -0,0 +1,13 @@
+CPP        = cpp -traditional-cpp $(GFLAGS)
+
+include $(GENERAL_RULES)/standard
+## include $(GENERAL_RULES)/Pgi/openmp
+
+ifneq (,$(findstring ~openmp,$(WM_COMPILE_CONTROL)))
+    include $(GENERAL_RULES)/no-openmp
+endif
+
+include $(DEFAULT_RULES)/c
+include $(DEFAULT_RULES)/c++
+
+# -----------------------------------------------------------------------------

wmake/rules/linux64Nvidia/mplibOPENMPI

@@ -0,0 +1,3 @@
+PFLAGS     = -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX
+PINC       = -I$(MPI_ARCH_PATH)/include
+PLIBS      = -L$(MPI_ARCH_PATH)/lib$(WM_COMPILER_LIB_ARCH) -L$(MPI_ARCH_PATH)/lib -lmpi

wmake/rules/linuxARM64Arm/c++

@@ -1,7 +1,9 @@
+#------------------------------------------------------------------------------
 # A clang variant
+#------------------------------------------------------------------------------
 include $(GENERAL_RULES)/Clang/c++
 
-CC          = armclang++ -std=c++11
+CC          = armclang++ -std=c++14
 
 c++ARCH     = -mcpu=native -pthread
 
@@ -18,3 +20,5 @@ include $(GENERAL_RULES)/Clang/link-c++
 
 LINKLIBSO  += -armpl
 LINKEXE    += -armpl
+
+#------------------------------------------------------------------------------

wmake/rules/linuxARM64Fujitsu/c++

@@ -1,7 +1,9 @@
+#------------------------------------------------------------------------------
 # Fujitsu compiler - a clang variant
+#------------------------------------------------------------------------------
 include $(GENERAL_RULES)/Clang/c++
 
-CC          = FCC -std=c++11
+CC          = FCC -std=c++14
 
 c++ARCH     = -pthread
 
@@ -15,3 +17,5 @@ cctoo       = $(Ctoo)
 cpptoo      = $(Ctoo)
 
 include $(GENERAL_RULES)/Clang/link-c++
+
+#------------------------------------------------------------------------------