Fix HOST_CROSS_OUT

Previously, HOST_CROSS_OUT was defined with the assumption that
windows_x86 is the only supported OS/Arch. In preparatio for Linux/ARM
support, HOST_CROSS_OUT is now defined using HOST_CROSS_OS and
HOST_CROSS_ARCH.

Bug: 159685774
Test: m

Change-Id: I0831c2885db37c44af4fd47bab8481bc885b4b7e