user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/tests/rtld/noload-promote/libfoo.c

@@ -0,0 +1 @@
+void foo() {}

user/include/mlibc/tests/rtld/noload-promote/meson.build

@@ -0,0 +1,5 @@
+libfoo = shared_library('foo', 'libfoo.c')
+test_depends = [libfoo]
+
+libfoo_native = shared_library('native-foo', 'libfoo.c', native: true)
+test_native_depends = [libfoo_native]

user/include/mlibc/tests/rtld/noload-promote/test.c

@@ -0,0 +1,24 @@
+#include <dlfcn.h>
+#include <assert.h>
+#include <stddef.h>
+
+#ifdef USE_HOST_LIBC
+#define LIBFOO "libnative-foo.so"
+#else
+#define LIBFOO "libfoo.so"
+#endif
+
+int main() {
+	void *foo = dlopen(LIBFOO, RTLD_LOCAL | RTLD_NOW);
+	assert(foo);
+
+	assert(dlsym(RTLD_DEFAULT, "foo") == NULL);
+
+	// Opening a library with RTLD_NOLOAD | RTLD_GLOBAL should promote it to the global scope.
+	assert(dlopen(LIBFOO, RTLD_NOLOAD | RTLD_GLOBAL | RTLD_NOW) == foo);
+	assert(dlsym(RTLD_DEFAULT, "foo") != NULL);
+
+	assert(dlopen("does-not-exist.so.1337", RTLD_NOLOAD | RTLD_GLOBAL | RTLD_NOW) == NULL);
+
+	return 0;
+}