Enable -Wmultichar.

-Wmultichar is enabled by default, so we don't need to explicitly
enable it.

Bug: 298703966
Test: presubmit
Change-Id: Iae820145e6412365024a97ab3a34d760563785fa
diff --git a/cc/config/global.go b/cc/config/global.go
index b662ef0..e5f2d2b 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -45,7 +45,6 @@
 		"-UDEBUG",
 
 		"-fno-exceptions",
-		"-Wno-multichar",
 
 		"-O2",
 		"-fdebug-default-version=5",