update_engine: Move -Wnon-virtual-dtor to CC flags

Since C does not have destructor, it makes more sense to more
-Wnon-virtual-dtor to CC.

BUG=none
TEST=emerge update_engine

Change-Id: Ic8a84b4354c4a4203589b06352befa09c4428975
Reviewed-on: https://chromium-review.googlesource.com/232934
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Nam Nguyen <namnguyen@chromium.org>
Tested-by: Nam Nguyen <namnguyen@chromium.org>
diff --git a/update_engine.gyp b/update_engine.gyp
index 236574e..f8d44bf 100644
--- a/update_engine.gyp
+++ b/update_engine.gyp
@@ -18,10 +18,10 @@
       '-Werror',
       '-Wno-unused-parameter',
       '-Wno-deprecated-register',
-      '-Wnon-virtual-dtor',
     ],
     'cflags_cc': [
       '-fno-strict-aliasing',
+      '-Wnon-virtual-dtor',
     ],
     'ldflags': [
       '-Wl,--gc-sections',