ENH: extend use of WM_COMPILER_CONTROL to manage compiler versions

- for compilers such as gcc and clang, may have several different
  variants installed on the computer. Use WM_COMPILER_CONTROL to
  specify the preferred variant.

  Eg,
      WM_COMPILER=Gcc
      WM_COMPILER_CONTROL="version=8"

      will compile with "gcc-8" and "g++-8"

  Good practice would be to tag output directory names with the
  version too. Eg

      WM_COMPILER=Clang110
      WM_COMPILER_CONTROL="version=11.0"

STYLE: modify message for change of gcc -> clang (darwin)

wmake/rules/linuxARM64Fujitsu/c

@@ -1,7 +1,9 @@
+#------------------------------------------------------------------------------
 # Fujitsu compiler - a clang variant
+#------------------------------------------------------------------------------
 include $(GENERAL_RULES)/Clang/c
 
-cc          = fcc
+cc          = fcc$(COMPILER_VERSION)
 
 cARCH       =
 
@@ -13,3 +15,5 @@ cFLAGS      = $(cARCH) $(GFLAGS) $(cWARN) $(cOPT) $(cDBUG) $(LIB_HEADER_DIRS) -f
 ctoo        = $(WM_SCHEDULER) $(cc) $(cFLAGS) -c $< -o $@
 
 include $(GENERAL_RULES)/Clang/link-c
+
+#------------------------------------------------------------------------------

wmake/rules/linuxARM64Fujitsu/c++

@@ -3,7 +3,7 @@
 #------------------------------------------------------------------------------
 include $(GENERAL_RULES)/Clang/c++
 
-CC          = FCC -std=c++14
+CC          = FCC$(COMPILER_VERSION) -std=c++14
 
 c++ARCH     = -pthread
 
@@ -12,9 +12,9 @@ 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)
+cxxtoo      = $(Ctoo)
 
 include $(GENERAL_RULES)/Clang/link-c++