intel/tools: Fix build with glibc < 2.27.

glibc < 2.27 defines OVERFLOW in /usr/include/math.h.

This patch fixes this build error.

In file included from ../include/c99_math.h:37:0,
                 from ../src/util/u_math.h:44,
                 from ../src/mesa/main/macros.h:35,
                 from ../src/intel/compiler/brw_reg.h:47,
                 from ../src/intel/tools/i965_asm.h:32,
                 from ../src/intel/tools/i965_gram.y:29:
src/intel/tools/i965_gram.tab.c:562:5: error: expected identifier before numeric constant
     OVERFLOW = 412,
     ^

Fixes: 70308a5a8a ("intel/tools: New i965 instruction assembler tool")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110656
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Acked-by: Eric Engestrom <eric@engestrom.ch>

src/intel/tools/i965_asm.h

@@ -36,6 +36,9 @@
 #include "compiler/brw_eu.h"
 #include "dev/gen_device_info.h"
 
+/* glibc < 2.27 defines OVERFLOW in /usr/include/math.h. */
+#undef OVERFLOW
+
 void yyerror (char *);
 int yyparse(void);
 int yylex(void);