Merging r294982:

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r294982 | arnolds | 2017-02-13 11:58:28 -0800 (Mon, 13 Feb 2017) | 6 lines

swiftcc: Don't emit tail calls from callers with swifterror parameters

Backends don't support this yet. They would have to move to the swifterror
register before the tail call to make sure it is live-in to the call.

rdar://30495920
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llvm-svn: 295219