Disable -Wc++-keyword because of false positives

This warning, a child category of -Wc++-compat, was causing a lot of
false positives of the following variety:

In file included from op.c:163:
In file included from ./perl.h:6228:
./proto.h:6124:26: warning: identifier 'wchar_t' conflicts with a C++ keyword [-Wc++-keyword]
 6124 | Perl_mbtowc_(pTHX_ const wchar_t *pwc, const char *s, const Size_t len);
      |                          ^
1 warning generated.

Author: Leont

cflags.SH

@@ -198,7 +198,7 @@ Intel*) ;; # # Is that you, Intel C++?
 	-Wextra \
 	-Wno-long-long -Wno-declaration-after-statement \
         -Wno-nonnull-compare \
-	-Wc++-compat -Wwrite-strings"
+	-Wc++-compat -Wno-c++-keyword -Wwrite-strings"
    case " $ccflags " in
    *" -std="*) ;; # Already have -std=...
    *) warns="-std=c99 $warns" ;;