Switch -w to -Wno-everything on C with GNU compilers

build/conf/compilers/gnu_compiler.conf

@@ -88,7 +88,7 @@ when ($NO_WSHADOW == "yes") {
 #
 # Use -Wno-everything to force warning suppression.
 when ($NO_COMPILER_WARNINGS == "yes") {
-    C_WARNING_OPTS = -w
+    C_WARNING_OPTS = -Wno-everything
     CXX_WARNING_OPTS = -Wno-everything
 }
 when ($NO_OPTIMIZE == "yes") {