st/mesa: allow st_format.h to be included from C++ files

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>

src/mesa/state_tracker/st_format.h

@@ -36,6 +36,10 @@
 #include "pipe/p_defines.h"
 #include "pipe/p_format.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct gl_context;
 struct pipe_screen;
 
@@ -77,4 +81,8 @@ st_translate_color(const union gl_color_union *colorIn,
                    union pipe_color_union *colorOut,
                    GLenum baseFormat, GLboolean is_integer);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* ST_FORMAT_H */