gallium/util: Wrap suballoc.h into extern C

Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7477>

src/gallium/auxiliary/util/u_suballoc.h

@@ -33,6 +33,10 @@
 
 struct u_suballocator;
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct u_suballocator *
 u_suballocator_create(struct pipe_context *pipe, unsigned size, unsigned bind,
                       enum pipe_resource_usage usage, unsigned flags,
@@ -46,4 +50,8 @@ u_suballocator_alloc(struct u_suballocator *allocator, unsigned size,
                      unsigned alignment, unsigned *out_offset,
                      struct pipe_resource **outbuf);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif