Merging r326235:

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r326235 | mstorsjo | 2018-02-27 11:42:19 -0800 (Tue, 27 Feb 2018) | 6 lines

[MinGW, CrossWindows] Allow passing -static together with -shared

In these combinations, link a DLL as usual, but pass -Bstatic instead
of -Bdynamic to indicate prefering static libraries.

Differential Revision: https://reviews.llvm.org/D43811
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llvm-svn: 333566