LLVM can now emit/parse/diff Windows PDBs

PDBs are the sidecar symbol files for Windows. The spec used to be private, now is public, and now it is great to see Clang supporting them. Last time I looked, GCC does not support them.

https://twitter.com/aionescu/status/898829293714784256

http://blog.llvm.org/2017/08/llvm-on-windows-now-supports-pdb-debug.html