tgsi_to_nir: add #ifdef header guards

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/gallium/auxiliary/nir/tgsi_to_nir.h

@@ -21,6 +21,9 @@
  * IN THE SOFTWARE.
  */
 
+#ifndef TGSI_TO_NIR_H
+#define TGSI_TO_NIR_H
+
 #include "compiler/nir/nir.h"
 #include "pipe/p_screen.h"
 
@@ -31,3 +34,5 @@ tgsi_to_nir(const void *tgsi_tokens,
 struct nir_shader *
 tgsi_to_nir_noscreen(const void *tgsi_tokens,
                      const nir_shader_compiler_options *options);
+
+#endif