libselinux: fix subdir build and usage of cmdline CFLAGS

commit 16c123f4b1f3c8d20b3f597df161d7e635620923 ("libselinux:
support ANDROID_HOST=1 on Mac") broke the ability to run make
in the src subdirectory of libselinux (because OS and COMPILER
were not defined) and also caused some warning flags that could
be overridden via command-line CFLAGS to be mandatory.  Fix it.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
2 files changed