[clang][Tooling] Add support for .rsp files in compile_commands.json

Summary:
Add support for .rsp files.

Fixes https://github.com/clangd/clangd/issues/81

Patch By: liu hui(@lh123)

Reviewers: sammccall, ilya-biryukov, hokein, kadircet

Reviewed By: kadircet

Subscribers: merge_guards_bot, mgorny, MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang-tools-extra, #clang

Differential Revision: https://reviews.llvm.org/D70222