[llvm] r223802 - IR: Split Metadata from Value

[Hans Wennborg]

This broke the MSVC build, see e.g. [1]. I suspect it is because MSVC
(except recent versions) doesn't support LLVM_EXPORTED. I tried
removing those operator bool()'s, but there were more errors.

Does your patch compile if you remove LLVM_EXPORTED? I suspect that
might reveal the same problem on Mac/Linux.

 - Hans

 1. http://build.chromium.org/p/chromium.fyi/builders/CrWinClang/builds/660/steps/runhooks/logs/stdio