Use source directories for toolchain includes and wrapper tools

[dzbarsky]

Compile and linker action inputs should now be fully optimized:

➜  tests git:(zbarsky/toolchain) bazel cquery --output=files @llvm_toolchain_with_sysroot//:compiler-files-aarch64-darwin
INFO: Found 1 target...
external/toolchains_llvm++llvm+llvm_toolchain_llvm/include/c++
external/toolchains_llvm++llvm+llvm_toolchain_llvm/lib/clang/16/include
external/toolchains_llvm++llvm+llvm_toolchain_llvm/bin/clang
external/toolchains_llvm++llvm+llvm_toolchain_llvm/bin/clang++
external/toolchains_llvm++llvm+llvm_toolchain_llvm/bin/clang-cpp
external/toolchains_llvm++llvm+llvm_toolchain_with_sysroot/bin
INFO: Elapsed time: 0.308s, Critical Path: 0.00s
INFO: 0 processes.
INFO: Build completed successfully, 0 total actions

I'm not sure why ar is in the linker files, perhaps it can be removed.

➜  tests git:(zbarsky/toolchain) bazel cquery --output=files @llvm_toolchain_with_sysroot//:linker-files-aarch64-darwin
INFO: Found 1 target...
➜  tests git:(zbarsky/toolchain) ✗ bazel cquery --output=files @llvm_toolchain_with_sysroot//:linker-files-aarch64-darwin        
INFO: Invocation ID: d6b673ec-b86d-413d-808b-1e8eda884ad0
INFO: Analyzed target @@toolchains_llvm++llvm+llvm_toolchain_with_sysroot//:linker-files-aarch64-darwin (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
external/toolchains_llvm++llvm+llvm_toolchain_llvm/bin/clang
external/toolchains_llvm++llvm+llvm_toolchain_llvm/bin/clang++
external/toolchains_llvm++llvm+llvm_toolchain_llvm/bin/clang-cpp
external/toolchains_llvm++llvm+llvm_toolchain_llvm/bin/ld.lld
external/toolchains_llvm++llvm+llvm_toolchain_llvm/bin/ld64.lld
external/toolchains_llvm++llvm+llvm_toolchain_llvm/bin/wasm-ld
external/toolchains_llvm++llvm+llvm_toolchain_llvm/bin/llvm-ar
external/toolchains_llvm++llvm+llvm_toolchain_llvm/lib/clang/16/lib
external/toolchains_llvm++llvm+llvm_toolchain_llvm/lib/libc++.a
external/toolchains_llvm++llvm+llvm_toolchain_llvm/lib/libc++abi.a
external/toolchains_llvm++llvm+llvm_toolchain_llvm/lib/libc++experimental.a
external/toolchains_llvm++llvm+llvm_toolchain_llvm/lib/libunwind.a
external/toolchains_llvm++llvm+llvm_toolchain_with_sysroot/bin
INFO: Elapsed time: 0.108s, Critical Path: 0.00s