Only turn on -pedantic for compilers that support it.

configure.in

@@ -2414,7 +2414,9 @@ AC_SUBST(COMPILER_DEPEND)
 AC_SUBST(MDDEPDIR)
 
 dnl Make pedantic a flag for now since the builds currently choke on it.
-_PEDANTIC=1
+if test "$GNU_CC"; then
+    _PEDANTIC=1
+fi
 MOZ_ARG_DISABLE_BOOL(pedantic,
 [  --disable-pedantic      Issue all warnings demanded by strict ANSI C ],
   _PEDANTIC= )