Made 'make install' include libs for additional targets

[dmski]

'make install' didn't actually install libs for additional targets, which resulted in installed rustc being unable to cross-compile with an error saying 'unable to find crate std'.

[alexcrichton]

cc @brson

Have you tested this to ensure that all the targets are installed from make install and make dist? We don't have many tests for this part of the build system, sadly. I'm also curious why windows wasn't updated?

[brson]

This behavior is intentional for dist and an oversight for install. I specifically did not want to include 32 bit libs in 64 bit installers because they are not very useful.

[dmski]

@alexcrichton i did test with --target=arm-linux-androideabi on macos-x86_64 and verified that libs for both archs get installed and rustc can produce binaries for both. As to windows - i somehow just missed it. Have pushed an update.

[dmski]

@brson ok, thanks for clarification, i'll try just fixing install then.

[dmski]

I've pushed an update which makes make install install additional target libs leaving the old make dist behaviour. I've checked that after being configured with --target=arm-linux-androideabi on macos-x86_64 make install installs arm libs into rustlib and that make dist produces tarball and macos pkg containing only libs for x86_64. Does this look ok? Are there any other targets/scenarios that need to be checked?