Add 'extern "C"' to error.h.

src/core/lib/iomgr/error.h

@@ -40,6 +40,10 @@
 #include <grpc/status.h>
 #include <grpc/support/time.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /// Opaque representation of an error.
 /// Errors are refcounted objects that represent the result of an operation.
 /// Ownership laws:
@@ -204,4 +208,8 @@ bool grpc_log_if_error(const char *what, grpc_error *error, const char *file,
 #define GRPC_LOG_IF_ERROR(what, error) \
   grpc_log_if_error((what), (error), __FILE__, __LINE__)
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* GRPC_CORE_LIB_IOMGR_ERROR_H */