Libraries: Create top level directory for libraries.

Things were getting a little crowded in the project root, so this patch
moves the Lib*/ directories into Libraries/.

Libraries/LibC/setjmp.h

@@ -0,0 +1,25 @@
+#pragma once
+
+#include <signal.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <sys/cdefs.h>
+#include <sys/types.h>
+
+__BEGIN_DECLS
+
+struct __jmp_buf {
+    uint32_t regs[6];
+    bool did_save_signal_mask;
+    sigset_t saved_signal_mask;
+};
+
+typedef struct __jmp_buf jmp_buf[1];
+
+int setjmp(jmp_buf);
+void longjmp(jmp_buf, int val);
+
+int sigsetjmp(jmp_buf, int savesigs);
+void siglongjmp(jmp_buf, int val);
+
+__END_DECLS