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/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++
+
+#------------------------------------------------------------------------------