For cross-compiling on Android, some specific changes are needed in
the Makefile.

Update the Makefile to support cross-compiling for Android.
The original ideea for this was send by Bernhard Rosenkraenzer in
https://lkml.org/lkml/2012/8/23/316, but this is a rewrite.

Changes:
() support bionic in addition to glibc
() remove rt and pthread libraries that do not exist in Android
() use $(CFLAGS) when detecting initial compiler flags. This is needed
when setting CFLAGS as an argument of make (e.g. for setting --sysroot).
() include perf's local directory when building for Android to be able to find
relative paths if using --sysroot (e.g.: ../../include/linux/perf_event.h)
Signed-off-by: NIrina Tirdea <irina.tirdea@intel.com>
Cc: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1349678613-7045-3-git-send-email-irina.tirdea@gmail.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>