CONFIG: improve support for compiler/link options (#1830)

- introduce WM_COMPILE_CONTROL variable to convey control information
  into the build rules.

  The convention (as per spack):
      - '+' to select a feature
      - '~' to deselect a feature

  Eg, to select the gold linker, and disable openmp
  (spaces are not required):

      WM_COMPILE_CONTROL="+gold ~openmp"

CONFIG: accept FOAM_EXTRA_LDFLAGS for AMD, gold, Mingw linkers

CONFIG: generalize PROJECT_LIBS (-ldl used almost universally)

wmake/rules/linux64Mingw/c++

@@ -19,7 +19,7 @@ LINK_LIBS   = $(c++DBUG)
 # Using "-Wl,--no-undefined,--enable-runtime-pseudo-reloc"
 # does not forgive undefined symbols during linking
 
-LINKLIBSO   = $(CC) $(c++FLAGS) \
+LINKLIBSO   = $(CC) $(c++FLAGS) -shared \
     -Wl,--output-def=$(LIB).def \
     -Wl,--out-implib=$(LIB).dll.a \
     -Wl,--no-undefined \
@@ -27,9 +27,10 @@ LINKLIBSO   = $(CC) $(c++FLAGS) \
     -Wl,--enable-auto-import \
     -Wl,--enable-auto-image-base \
     -Wl,--strip-all \
-    -shared
+    $(FOAM_EXTRA_LDFLAGS)
 
 LINKEXE     = $(CC) $(c++FLAGS) \
     -Wl,--enable-auto-import \
     -Wl,--strip-all \
-    -Wl,--force-exe-suffix
+    -Wl,--force-exe-suffix \
+    $(FOAM_EXTRA_LDFLAGS)

wmake/rules/linux64Mingw/general

@@ -6,7 +6,8 @@ LD      = x86_64-w64-mingw32-ld
 AR      = x86_64-w64-mingw32-ar
 RANLIB  = x86_64-w64-mingw32-ranlib
 
-PROJECT_LIBS = -l$(WM_PROJECT) -L$(FOAM_LIBBIN)/dummy -lPstream
+PROJECT_LIBS = -l$(WM_PROJECT) \
+    -L$(FOAM_LIBBIN)/dummy -lPstream
 
 include $(GENERAL_RULES)/standard