Merging r328039:

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r328039 | mstorsjo | 2018-03-20 13:37:51 -0700 (Tue, 20 Mar 2018) | 8 lines

[X86] Don't use the MSVC stack protector names on mingw

Mingw uses the same stack protector functions as GCC provides
on other platforms as well.

Patch by Valentin Churavy!

Differential Revision: https://reviews.llvm.org/D27296
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llvm-svn: 332001