CONFIG: add support for WM_COMPILE_OPTION='Dbg'

- uses '-g -DFULLDEBUG' (like Debug), but with -O3 (like Opt).

  This adds in debug symbols and FULLDEBUG code segments (good for
  code development) but retains -O3 optimizations and code paths and
  avoids the much slower -O0 associated with 'Debug'.

- add in central wmake/General/common/{c,c++}XXX tuning,
  which helps reduce the number of nearly identical files

ENH: add support for wmake -debug-Og

wmake/rules/linuxClang/c++

@@ -1,9 +1,11 @@
 #------------------------------------------------------------------------------
 include $(GENERAL_RULES)/Clang/c++
 
-c++ARCH     = -m32 -pthread
+c++ARCH    := -m32 -pthread
 
-include $(DEFAULT_RULES)/c++$(WM_COMPILE_OPTION)
+ifneq (,$(WM_COMPILE_OPTION))
+    sinclude $(DEFAULT_RULES)/c++$(WM_COMPILE_OPTION)
+endif
 
 c++FLAGS    = \
     $(c++ARCH) $(GFLAGS) $(c++WARN) $(c++OPT) $(c++DBUG) $(ptFLAGS) \