mesa: Prevent collision of ERROR define on Windows.

This issue might recur on other OSes. If so then it might be better
to remove the C-preprocessor magic, and use fully qualified defines
instead.

Signed-off-by: Dave Airlie <airlied@redhat.com>

src/mesa/main/errors.c

@@ -55,6 +55,9 @@ static char out_of_memory[] = "Debugging error: out of memory";
 #define source_is(s, kind) enum_is(s, SOURCE, kind)
 #define type_is(t, kind) enum_is(t, TYPE, kind)
 
+/* Prevent define collision on Windows */
+#undef ERROR
+
 enum {
    SOURCE_APPLICATION,
    SOURCE_THIRD_PARTY,