user: implement mlibc as the libc, finally.

It's finally done..

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

ext2_root/usr/include/errno.h

@@ -0,0 +1,31 @@
+#ifndef _ERRNO_H
+#define _ERRNO_H
+
+#include <abi-bits/errno.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef __MLIBC_ABI_ONLY
+
+/* Some programs define their own errno as an "extern int" if it is not a macro. */
+#define errno __mlibc_errno
+extern __thread int __mlibc_errno;
+
+int *__errno_location(void);
+
+/* Linux extensions. */
+
+extern char *program_invocation_name;
+extern char *program_invocation_short_name;
+extern char *__progname;
+extern char *__progname_full;
+
+#endif /* !__MLIBC_ABI_ONLY */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _ERRNO_H */