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.c

@@ -0,0 +1,35 @@
+#include <stdio.h>
+
+int
+main(int argc, char** argv) {
+	FILE *fp;
+	int i;
+	char * output = "/tmp/io-test.txt";
+
+	if(argc == 2){
+		output = argv[1];
+	}else if(argc > 2){
+		printf("usage: %s [output]", argv[0]);
+		return 100;
+	}
+
+	fp = fopen(output, "w+");
+	if(fp == NULL){
+		printf("Can't open %s", output);
+		return 1;
+	}
+	i = fprintf(fp, "%s works.\n", "fprintf");
+	if(i <= 0){
+		fclose(fp);
+		printf("Can't write 'fprintf works.' to %s", output);
+		return 2;
+	}
+	i = fputs("fputs works.\n", fp);
+	if(i == EOF){
+		fclose(fp);
+		printf("Can't write 'fputs works.' to %s", output);
+		return 3;
+	}
+	fclose(fp);
+	return 0;
+}