user: implement mlibc as the libc, finally.

It's finally done..

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

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

@@ -0,0 +1,19 @@
+#include <assert.h>
+#include <libgen.h>
+#include <string.h>
+
+int main() {
+	/* intentionally a macro: basename modifies its argument */
+#define test_string(x, expectval) do {                         \
+		char str[] = x;                                \
+		assert(strcmp(basename(str), expectval) == 0); \
+	} while (0)
+
+	test_string("/usr/lib", "lib");
+	test_string("/usr/", "usr");
+	test_string("/", "/");
+	test_string(".", ".");
+	test_string("..", "..");
+
+	return 0;
+}