Enable enum-enum-conversion warning

Test: presubmit
Bug: 154138986
Change-Id: I1076e732118c138774ab377adc3273a41f7dde08
diff --git a/cc/config/global.go b/cc/config/global.go
index 0f31931..a4627b2 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -224,7 +224,6 @@
 		"-Wno-deprecated-anon-enum-enum-conversion", // http://b/153746485
 		"-Wno-deprecated-enum-enum-conversion",      // http://b/153746563
 		"-Wno-string-compare",                       // http://b/153764102
-		"-Wno-enum-enum-conversion",                 // http://b/154138986
 		"-Wno-pessimizing-move",                     // http://b/154270751
 		// New warnings to be fixed after clang-r399163
 		"-Wno-non-c-typedef-for-linkage", // http://b/161304145