Log Message:
Overhaul the way packages can ask for "msgfmt".  If a package needs
msgfmt, then it should set the following in the package Makefile:

	USE_TOOLS+=	msgfmt

To deal with message files that use the "msgid_plural" statement,
which isn't supported in NetBSD<=3.x and also in gettext<=0.10.35, we
determine if the built-in "msgfmt" is sufficiently new enough to
understand "msgid_plural".  If it isn't, then we use the msgfmt.sh
script to transform the msgid_plural statements to an equivalent
construct that's understood by older msgfmt tools.

The msgfmt.sh script is a straightforward translation of the original
perl script msgfmt.pl script by Julio M. Merino Vidal into shell and
awk, which are more lightweight dependencies than perl.

We remove the USE_MSGFMT_PLURALS bits in gettext-lib/builtin.mk as they
are made obsolete by the new code in mk/tools/msgfmt.mk.

BUILD_USE_MSGFMT is still supported but will be removed in a separate
commit.