Tell Soong about HOST_CROSS_*

This configures Soong to build windows binaries, which requires support
for 64-bit windows binaries in BUILD_PREBUILT for USE_SOONG=true.

module_arch_supported.mk did not support 64-bit being the secondary
architecture when evaluating multilib conditionals. All other uses of
HOST_*_IS_64_BIT already check the proper version.

Change-Id: Iff664733e6991f4adbe8ddd620b091bbb55d1d86