Minor fixes to convert-keymap.pl (conversion of 8bit characters in the form
'x' with high bit set) and to KBDFILES.map (fix encodings and comment out a
few redundant keymap files).

MFC after:	3 days
Fix minor problems found while converting to NEWCONS format.

MFC after:	3 days
Make note about reset vs RTOE actions...
Create the native-xtools target. This target creates only the cross
building toolchain for the host computer. This toolchain produces
TARGET_ARCH and assumes the rest of the system contains libraries for
the target. It is intended to be used in a "qemu-user jail" where all
the binaries would otherwise be the target architecture's to build
ports. However, emulation of the compilers is too slow, so we build
native binaries for that. Rather than use the xdev produced binaries,
with all their weird links and paths, these binaries use the native
paths. They will not work unless installed into the qemu-user jail.

Differential Revision: https://phabric.freebsd.org/D518
Reviewed by: sbruno@
Fix a few conversion problems (e.g. when a keymap is derived from ISO8859-1,
but shall provide an Euro sign - similar for Japanese Yen).

The Brazilian keymap "br.kbd" now has accents, by default - the no-accents
version has been renamed to "br.noacc.kbd".

MFC after:	3 days