user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/options/ansi/generic/errno.cpp

@@ -0,0 +1,12 @@
+#include <errno.h>
+
+int __thread __mlibc_errno;
+
+char *program_invocation_name = nullptr;
+char *program_invocation_short_name = nullptr;
+extern char *__progname __attribute__((__weak__, __alias__("program_invocation_short_name")));
+extern char *__progname_full __attribute__((__weak__, __alias__("program_invocation_name")));
+
+int *__errno_location() {
+	return &__mlibc_errno;
+}