qa: introduce runners and more tests for newlib

For each test, if a script exists with the same name of the test
plus the .runner suffix, the runner is run instead of the test.

As a first example qa/lib/newlib/testsuite/atexit is run by
qa/lib/newlib/testsuite/atexit.runner.

These .runner scripts allow more complex checks of the side effects
generated by the test.

qa/lib/newlib/100-files.runner

@@ -0,0 +1,18 @@
+#!/cmd/rc
+runner=$0
+test = `{echo $runner|sed 's/.runner//'}
+test_output = /tmp/output-`{basename $test}
+
+if ( test -e $test_output) rm $test_output
+
+$test $test_output > /dev/null
+if ( cat $test_output | grep 'fprintf works.' > /dev/null ) {
+	if ( cat $test_output | grep 'fputs works.' > /dev/null ) {
+		rm $test_output
+		echo PASS
+		exit PASS
+	}
+}
+cat $test_output
+echo FAIL
+exit FAIL