Forbid -Weverything

Use of -Weverything blocks build system changes and toolchain updates
on new warnings.  Forbid it in the build system.  Developers can
experiment with -Weverything on their module by adding it to their
Android.mk file and building with
m ANDROID_TEMPORARILY_ALLOW_WEVERYTHING=true

Fixes: 143713277
Test: manual
Change-Id: Ifca9ad45301b0d51f18b5ae85cfb9e5b89fbef3f