[llvm] [CMake][gRPC] Update FindGRPC.cmake to support newer gRPC versions (PR #162935)

[Steven Wu via llvm-commits]

cachemeifyoucan wrote:

I tested on macOS, where it seems no extra settings are needed to find gRPC as long as the package is installed via HomeBrew.

I don't know if there are anyone relies on the linking system library path, which obvious missing all the dependencies if using any recent gRPC version as reported in the GitHub issues linked. Maybe it can be removed.

https://github.com/llvm/llvm-project/pull/162935