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Rather than telling gcc to make warnings as errors, and then hunting
down make rules to disable this, leave them as warnings, but invoke
gcc through a wrapper that checks the warnings against a whitelist.

The initial whitelist comes from the warnings in the current build,
all of which have been allowed through Make overrides.

Change-Id: Ifc9952e03d1a5dbcd90819dc7aa0ec7e50328e20
Signed-off-by: David Brown <davidb@codeaurora.org>
(cherry picked from commit d21ced2f0dda815cac69c693cd81e2e75d8f0007)