Set cmake_snapshot_supported for musl crt objects

Cmake snapshots are not supported for musl, but all host modules
have a dependency on the musl crt objects when the host is building
for musl.  Set cmake_snapshot_supported: true on the CRT objects to
avoid triggering a "CMake snapshots not supported, despite being a
dependency for..." error.

Bug: 190084016
Test: m USE_HOST_MUSL=true nothing
Change-Id: Ibca277f8e697dd1e22a232414202061007ff61ec