global: Disable deprecated-non-prototype warning with clang

We have a number of places in the code which use the following syntax:

void func(a, b, c)
    int a; /* Does a */
    something_t *b; /* Pointer to b */
    int c; /* Does c */
{
...
}

Which while not what we document as our coding style, this is also code
which we have imported from other projects, and would like to re-sync
with in the future. While the biggest example of this is the zlib code,
there are other places as well. For now, we will silence this warning.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

Makefile

@@ -790,6 +790,7 @@ KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
 # See modpost pattern 2
 KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
 KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)
+KBUILD_CFLAGS += $(call cc-disable-warning, deprecated-non-prototype)
 endif
 
 # These warnings generated too much noise in a regular build.