Generate a clang CompilationDatabase when running CMake

This generates a compile_commands.json file, which tells tools like
YouCompleteMe and clang_complete exactly how to build each source file.

Patch by Justin Lebar!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255789 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed