perf tools: Remove noise in python version feature test

Now that the feature tests honours the V=1 make verbosity switch, add a
return to the main() routine in the python version test, to avoid this
distraction:

CHK python version
<stdin>: In function 'main':
<stdin>:5: warning: control reaches end of non-void function

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-999no5yxlc2oqo9xjeez5zmv@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/config/feature-tests.mak

@@ -121,7 +121,10 @@ define SOURCE_PYTHON_VERSION
 #if PY_VERSION_HEX >= 0x03000000
 	#error
 #endif
-int main(void){}
+int main(void)
+{
+	return 0;
+}
 endef
 define SOURCE_PYTHON_EMBED
 #include <Python.h>