NetBSD re-synchronization of the source tree

This brings our tree to NetBSD 7.0, as found on -current on the
10-10-2015.

This updates:
- LLVM to 3.6.1
- GCC to GCC 5.1
- Replace minix/commands/z

NetBSD re-synchronization of the source tree

This brings our tree to NetBSD 7.0, as found on -current on the
10-10-2015.

This updates:
- LLVM to 3.6.1
- GCC to GCC 5.1
- Replace minix/commands/zdump with usr.bin/zdump
- external/bsd/libelf has moved to /external/bsd/elftoolchain/
- Import ctwm
- Drop sprintf from libminc

Change-Id: I149836ac18e9326be9353958bab9b266efb056f0

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Adjust boot from NetBSD.

- Add load_mods command to boot2 (load_mods /dir/mod*).
- Rename resulting binary to boot_monitor.
- Change default banner when used in MINIX.

Initial import of libsa, libkern, bootxx, boot.