Disable mixed builds for non-device OS

We don't currently support propagation of OS in mixed builds, and our
host toolchains are not properly configured.

This allows us to continue to make progress on device OS until host is
supported.

Test: mixed_libc CI
Test: USE_BAZEL_ANALYSI=1 m adbd
Change-Id: I2bf8b3f9ca7928dd33bf2fb3d4fa067da0f593f3