Clean up use of HAVE_ANDROID_OS

HAVE_ANDROID_OS was defined as "1" for targets, but never defined as "0"
for non-targets. Changing them to #ifdef should be safe and matches
all the other uses of HAVE_ANDROID_OS throughout the system.

Change-Id: I82257325a8ae5e4e4371ddfc4dbf51cea8ea0abb