swift

1e76df78 - Use toolchain clang on macOS

Use toolchain clang on macOS Don't use the just-built clang on macOS. macOS does this more "right" than the Linux build. Linux will sometimes use the just-built Swift-driver with the just-built clang, but sometimes would use the system clang instead. macOS uses the toolchain Swift-driver with the toolchain clang. This is correct, but it means that if we force the other clang, we'll get mismatched sanitizer runtimes so the ASAN bot will fail. (cherry picked from commit f446c25e0cc01dc1d66b2e2046c6b385baf38455)