Lots of minor compat stuff while seeing if bash would build.

We're quite far from bash building, but we'll get there eventually!

LibC/fcntl.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#define F_DUPFD 0
+#define F_GETFD 1
+#define F_SETFD 2
+#define F_GETFL 3
+#define F_SETFL 4
+
+__END_DECLS