Merging r314070:

Merging r314070:
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r314070 | dylanmckay | 2017-09-24 14:07:26 +1300 (Sun, 24 Sep 2017) | 6 lines

[AVR] Implement getCmpLibcallReturnType().

This fixes the avr-rust issue (#75) with floating-point comparisons generating broken code.
By default, LLVM assumes these comparisons return 32-bit values, but ours are 8-bit.

Patch By Thomas Backman.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_50@314357 91177308-0d34-0410-b5e6-96231b3b80d8