Partially import gcc and binutils

They are used as build tools for cross compilation. This import does
not include the full distribution. Rather, it sports a shell script
that will download and patch the distribution when compiled from
/usr/src/tools (yet to be committed). This part of the source tree is
only necessary for cross compilation. It's not used or compiled for
native builds.
Import NetBSD byacc
Import NetBSD flex
Import NetBSD make
Import NetBSD mktemp
Import NetBSD mtree

mtree is only used for cross compilation at this point. Also, the
required patches to make it compile on Minix cripple it probably
enough to make it unusable anyway.
Import NetBSD xinstall

Also, fix mk files for cross compilation.
Fix sed for cross compilation
Remove duplicate sed
Import NetBSD tools and build.sh

This commit finalizes support for cross compilation. The tools
directory are all links to the actual tools and are built on the
host system to build Minix. build.sh is the work horse that takes
care of all environment settings. It's slightly adjusted for Minix.
The /usr/src/Makefile has additional targets needed for cross
compilation.
Update gitignore for releasetools
xinstall fix for cross compilation
Build file cross compilation tool
Update nbsd_ports to account for new utils
Not every shell understands 'let'
Make mkfs.mfs cross compilable
Cross compile MFS ramdisk
Clean up generated files for ash,ramdisk,libutil,libc
Don't build ext2 ramdisk for cross compilation

. as mkfs.mfs is now cross compilable, we can remove the ext2 ramdisk
  special case for cross compilation.
mkfs.mfs: no need to include a.out.h