BuildSystem: Move all userpace libraries under the userspace directory

As the number of libraries is increasing, root directory starts to
expand. This adds better organization for libraries

userspace/libraries/LibC/include/setjmp.h

@@ -0,0 +1,20 @@
+#ifndef _SETJMP_H
+#define _SETJMP_H 1
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/setjmp.h.html
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+typedef int jmp_buf[1];
+typedef int sigjmp_buf[1];
+
+void	longjmp(jmp_buf env, int val);
+void	siglongjmp(sigjmp_buf env, int val);
+int		setjmp(jmp_buf env);
+int		sigsetjmp(sigjmp_buf env, int savemask);
+
+__END_DECLS
+
+#endif