Merging r326476:

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r326476 | mstorsjo | 2018-03-01 12:22:57 -0800 (Thu, 01 Mar 2018) | 7 lines

[RecordLayout] Only assert that fundamental type sizes are power of two on MSVC

Make types with sizes that aren't a power of two an error (that can
be disabled) in structs with ms_struct layout, except on mingw where
the situation is quite likely to occur and GCC handles it silently.

Differential Revision: https://reviews.llvm.org/D43908
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llvm-svn: 333571