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/General/Pgi/link-c++

@@ -1,5 +1,8 @@
 LINK_LIBS   = $(c++DBUG)
 
-LINKLIBSO   = $(CC) $(c++FLAGS) -shared $(FOAM_EXTRA_LDFLAGS)
+LINKLIBSO   = $(CC) $(c++FLAGS) -shared \
+    $(FOAM_EXTRA_LDFLAGS)
 
-LINKEXE     = $(CC) $(c++FLAGS) -Xlinker --add-needed $(FOAM_EXTRA_LDFLAGS)
+LINKEXE     = $(CC) $(c++FLAGS) \
+    -Xlinker --add-needed \
+    $(FOAM_EXTRA_LDFLAGS)