add test to check that all NDK headers are C compatible and warning free

[DanAlbert]

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Description

I was fairly certain we already had this test, but we should verify this so that we don't have problems like https://github.com/android/ndk/issues/1739 again

[jmgao]

versioner compiles headers as both gnu++11 and gnu11 (#440), with -Weverything so I'd guess it's not getting run for all of the NDK headers?

[DanAlbert]

It's only libc (and only the core libc headers at that), and we're trying to get rid of versioner since it prevents https://github.com/android/ndk/issues/837 from working on those headers.

I suppose we could leave it but disable the preprocessing part of what it does, but I think it's probably not too hard to just write a test that does this (or modify ndk_headers to verify this).