[PATCH v1] Merge common attribute handling code between libgccjit and c-family.

[David Malcolm via Sourceware Forge]

The overall idea looks good to me from a libgccjit maintainer point-of-view, though I didn't painstakingly check every hunk of the move.

@jsm28 : what do you think from a C maintainer/global review POV?

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https://forge.sourceware.org/gcc/gcc/pulls/207#issuecomment-7212