util: add c++ guards to u_mm.h

Needed for gfxstream.

Reviewed-by: Marcin Radomski <dextero@google.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32015>

src/util/u_mm.h

@@ -29,10 +29,12 @@
  * heaps, etc.
  */
 
-
 #ifndef _U_MM_H_
 #define _U_MM_H_
 
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 struct mem_block {
    struct mem_block *next, *prev;
@@ -88,4 +90,8 @@ extern void u_mmDestroy(struct mem_block *mmInit);
  */
 extern void u_mmDumpMemInfo(const struct mem_block *mmInit);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif