r600: protect r600_isa.h with extern "C"

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
diff --git a/src/gallium/drivers/r600/r600_isa.h b/src/gallium/drivers/r600/r600_isa.h
index b3f49bd..005b580 100644
--- a/src/gallium/drivers/r600/r600_isa.h
+++ b/src/gallium/drivers/r600/r600_isa.h
@@ -29,6 +29,10 @@
 
 #include "util/u_debug.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* ALU flags */
 enum alu_op_flags
 {
@@ -1236,4 +1240,8 @@
 	return op - 1;
 }
 
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
 #endif /* R600_ISA_H_ */