tests: keep the rename-flags helper compiling off Linux

renameat2 and its flags are Linux-only; the integration tests are
skipped elsewhere, so the helper just reports the commands as
unsupported.

Author: matejk

tests/helpers/fsops_helper.c

@@ -31,6 +31,7 @@ int main(int argc, char **argv)
 	}
 
 	if (!strcmp(argv[1], "noreplace") || !strcmp(argv[1], "exchange")) {
+#ifdef __linux__
 		unsigned int flags = !strcmp(argv[1], "noreplace") ?
 			RENAME_NOREPLACE : RENAME_EXCHANGE;
 
@@ -39,6 +40,12 @@ int main(int argc, char **argv)
 			return 2;
 		}
 		return 0;
+#else
+		/* The integration tests only run on Linux; keep the helper
+		 * compiling on the other platforms. */
+		fprintf(stderr, "rename flags are not supported on this platform\n");
+		return 3;
+#endif
 	}
 
 	if (!strcmp(argv[1], "ftruncate")) {