Merging r369011:

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r369011 | bogner | 2019-08-15 17:36:13 +0200 (Thu, 15 Aug 2019) | 4 lines

[cmake] install_symlink should obey DESTDIR unconditionally

Setting DESTDIR was erroneously buried under a condition here - if
it's set it should always be used.
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llvm-svn: 369335