gallium/vl: Allow vl_zscan.h to be included from C++

Reviewed-by: Giancarlo Devich <gdevich@microsoft.com>
Reviewed-by: Ruijing Dong <ruijing.dong@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18328>

src/gallium/auxiliary/vl/vl_zscan.h

@@ -31,6 +31,10 @@
 #include "pipe/p_compiler.h"
 #include "pipe/p_state.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /*
  * shader based zscan and quantification
  * expect usage of vl_vertex_buffers as a todo list
@@ -100,4 +104,8 @@ vl_zscan_upload_quant(struct vl_zscan *zscan, struct vl_zscan_buffer *buffer,
 void
 vl_zscan_render(struct vl_zscan *zscan, struct vl_zscan_buffer *buffer, unsigned num_instances);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif