user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/tests/ansi/qsort.c

@@ -0,0 +1,31 @@
+#include <assert.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+static const char *arr[] = { "xyz", "abc", "ghi", "def" };
+
+static const size_t magic = 0xDEADBEEF;
+
+static int cmpstringp(const void *p1, const void *p2, void *ctx) {
+	/* The actual arguments to this function are "pointers to
+	 * pointers to char", but strcmp(3) arguments are "pointers
+	 * to char", hence the following cast plus dereference. */
+	assert(*(size_t *) ctx == magic);
+	return strcmp(*(const char **) p1, *(const char **) p2);
+}
+
+int main() {
+	qsort_r(&arr[0], sizeof(arr) / sizeof(*arr), sizeof(char *), cmpstringp, (void *) &magic);
+
+	assert(!strcmp(arr[0], "abc"));
+	assert(!strcmp(arr[1], "def"));
+	assert(!strcmp(arr[2], "ghi"));
+	assert(!strcmp(arr[3], "xyz"));
+
+	for(size_t i = 0; i < sizeof(arr) / sizeof(*arr); i++) {
+		fprintf(stderr, "%s\n", arr[i]);
+	}
+
+	return 0;
+}