android: Add host_cross_supported prop

Some modules are only intended to be build for the build host,
e.g. rust_library modules only used in rust_proc_macro or
code generators.

These should not be expected to be built for or supported on non-build
host platforms. Thus, add a host_cross_supported property to disable
the HostCross target.

Test: m blueprint_tests
Test: Modules with host_cross_supported: false don't build for HostCross
Change-Id: Ia15f55776e04d86aee19bb0dd0d27e1b985b2b75