Merging r294954 and r295592:

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r294954 | chapuni | 2017-02-13 06:59:53 -0800 (Mon, 13 Feb 2017) | 5 lines

Fix r291495 -- Normalize LLVM_CMAKE_PATH in clang standalone build.

CMake handles paths with slashes. It caused cmake/install failure on msbuild.exe.

Note, Other llvm-config-oriented variables have been normalized since they are stored in the cache attributed with PATH.
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r295592 | chapuni | 2017-02-18 19:17:31 -0800 (Sat, 18 Feb 2017) | 1 line

clang/CMakeLists.txt: Rework r294954 -- use file(TO_CMAKE_PATH).
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llvm-svn: 295760