s/Wno-error=unused-variable/Wno-unused-variable

http://b/315246135

Change-Id: I2086c644afc9a371732ccbe18d09fa078286ece0
diff --git a/cc/config/global.go b/cc/config/global.go
index a696367..168fc2f 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -254,7 +254,7 @@
 		"-Wno-pointer-to-int-cast",
 		"-Werror=fortify-source",
 		// http://b/315246135 temporarily disabled
-		"-Wno-error=unused-variable",
+		"-Wno-unused-variable",
 		// http://b/315250603 temporarily disabled
 		"-Wno-error=format",
 		// Disabled because it produces many false positives. http://b/323050926