Soong's multi-architecture building has grown complex, with the
combination of HostOrDevice+HostType+Arch necessary to determine how to
build a variant of a module, and three separate mutators to split each
into its variations.
Combine HostOrDevice+HostType into Os, which will be Linux, Darwin,
Windows, or Android. Store Os+Arch as a single Target.
Change-Id: Iae677eff61a851b65a7192a47f2dc17c1abb4160
For the x86_arm target, which uses two 32-bit architectures, x86
libraries should be installed into ".../lib", and arm libraries should
be installed into ".../lib/arm".
This shouldn't be necessary for binaries, but non-native binaries aren't
supported in Make right now, so we can revisit this once it's necessary.
Change-Id: I4d883c85d3ef4945ff6149d9c4fc81af5023e12b