Fix checks for Android.

__ANDROID__ is a define that comes from the toolchain when building
for Android targets. ANDROID has a different meaning. ANDROID is
defined for _every_ Android build, including those done for host
modules. For host modules, we want to build the regular Linux
sanitizers and builtins, not the one for Android devices. This hasn't
been a problem until now because we only just started building the
sanitizers for the host.