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/General/common/c++Debug

@@ -0,0 +1,6 @@
+#------------------------------------------------------------------------------
+
+c++DBUG    := -g -DFULLDEBUG
+c++OPT     := -O0
+
+#------------------------------------------------------------------------------