Build a musl sysroot zip

Build a musl sysroot into a zip file that can be used to populate
a prebuilt sysroot for building toolchains.

Bug: 190084016
Test: m USE_HOST_MUSL=true host-native
Change-Id: Ibc954c6a63970b78781a1a92c87ecff8142aff5f
1 file changed