ttn: Whitelist from -Werror=declaration-after-statement.

nir is the exception among gallium/auxiliary -- we don't need to compile
it with MSVC2008 yet.  And this enables us to use
-Werror=declaration-after-statement in the next commit as we should,
without complicated fixes to tgsi_to_nir module.

Trvial.  Tested with GCC and Clang.

src/gallium/auxiliary/nir/tgsi_to_nir.c

@@ -22,6 +22,10 @@
  * IN THE SOFTWARE.
  */
 
+#ifdef __GNUC__
+#pragma GCC diagnostic ignored "-Wdeclaration-after-statement"
+#endif
+
 #include "util/ralloc.h"
 #include "glsl/nir/nir.h"
 #include "glsl/nir/nir_control_flow.h"