build: split compiler-rt from WASI sysroot install
WASI sysroots installed libc++ and compiler-rt via the same runtimes mono build, leaving compiler-rt artifacts in the sysroot even though compiler-rt should belong under the compiler resource directory. That layout made it hard to package the WASI SDK correctly.
This patch modifies the WASI sysroot build to install compiler-rt under a separate resource directory so that we can copy the entire resource-dir's lib directory into the Swift resource dir.
