UPDATING: Adjust heading.
Fix some more things related to the switch to gcc47.

* Adjust make.conf and its manual page.

* Create gcc47 MLINKS properly (clean up the Makefile a bit, too).

* Exclude gcc44 in the qemu setup.
libm: Exclude -Woverflow from -Werror in s_csqrtl.c for gcc47/i386.

The issue is that a long double in gcc47 on i386 doesn't seem to be
able to hold LDBL_MAX. At least a warning is generated. Cause
unknown, might be a bug in gcc (or our gcc's configuration).

gcc47 on FreeBSD/i386 does not show this behavior (no warning
generated at least).

Until we have a better clue, don't turn this warning into an error,
even if -Werror is specified, so that building can go on.

FreeBSD-testing: tuxillo
Remove xlint. It's outdated and there are much better checkers around.

clang static analyzer, cppcheck, coccinelle et al.

So there's no need to maintain it in base.
Enable -Werror for world building with gcc47.

The kernel still has warnings to be reviewed.