user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/tests/posix/getcwd.c

@@ -0,0 +1,22 @@
+#include <assert.h>
+#include <limits.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+int main() {
+	char buf[PATH_MAX];
+	char *ret = getcwd(buf, PATH_MAX);
+
+	assert(ret);
+	assert((strlen(ret) == strlen(buf)) && strlen(ret));
+	assert(!strcmp(ret, buf));
+
+	char *ret2 = getcwd(NULL, 0);
+	assert(ret2);
+	assert(strlen(ret2));
+	assert(!strcmp(ret, ret2));
+	free(ret2);
+
+	return 0;
+}