When building with two OSes of the same class (Host, etc) enabled,
independently produce variants of each module for each OS, instead of
making `compile_multilib: "first"` select just one of the OSes.
My use case this is for Linux + LinuxBionic, which are both considered
Host class, but this would also applied if we wanted to generate rules
for Linux+Darwin, or some combination of firmware bits (either in
addition to Android in the Device Class, or multiple firmwares in a new
Class)
Bug: 31559095
Test: enable host bionic, see a linux(_glibc) and linux_bionic
definition for binaries
Change-Id: I55e7f046758b3dc2a31da2c4b20274ec68ece0a0