CONFIG: support wmake -debug-O0, -debug-O1 etc.

- rearranged order of flags so that FOAM_EXTRA_CXXFLAGS is added
  after the WARN/OPT/DBUG flags

CONFIG: drop wmake rules for PGI compiler (defunct)

wmake/rules/General/Nvidia/c

@@ -8,6 +8,6 @@ cc          = nvc$(COMPILER_VERSION)
 cARCH       =
 cDBUG       =
 cOPT        = -O2
-cWARN       = $(FOAM_EXTRA_CFLAGS)
+cWARN       =
 
 #------------------------------------------------------------------------------

wmake/rules/General/Nvidia/c++

@@ -10,15 +10,12 @@ c++DBUG     =
 c++OPT      = -O2
 ptFLAGS     = -DNoRepository
 
-# - Standard warnings
-# - Less restrictive warnings (may be needed for flex++, CGAL, etc.)
-
 c++WARN     = \
     -Wall -Wextra \
     --diag_suppress=111,128,177,185,612,998,1098 \
-    --display_error_number \
-    $(FOAM_EXTRA_CXXFLAGS)
+    --display_error_number
 
+# Less restrictive warnings (eg, for flex++, CGAL, etc.)
 c++LESSWARN =
 
 # Warnings