Use target.linux for all linux kernel based targets

Now in Android.bp files, target.linux applies to all targets running a
linux kernel (android, linux_glibc, linux_bionic). So common
flags/sources/etc can be combined instead of copying them to each
target.

Test: m
Change-Id: I02896fca358c7e27466d2c33e17a43f1b3af8665