Merging r370271:

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r370271 | tstellar | 2019-08-29 00:59:04 +0200 (Thu, 29 Aug 2019) | 6 lines

[LLVM-C] Fix omission of INSTALL_WITH_TOOLCHAIN to llvm_add_library()

Due to a misstake with r365902 that tried to simplify the install with
toolchain logic LLVM-C.dll was no longer being installed.

Patch By: Jakob Bornecrantz
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llvm-svn: 370306