Split the process to fetch GNU tools (until now embedded
within tools/Makefile.gnuhost) into a new Makefile.fetchgnu,
MINIX-specific hence relocated, which is to be also used
to fetch sources even when not building the tools.
Use it for binutils too.
Improve documentation.
Also do not run configure on each run when MKUPDATE=yes
The .WAIT serialization instruction between fetching and other
configure sources was raising a new run of configure at each
compilation. Avoid it by using two rules.
Change-Id: Ie24950ccbb5c5067f3c1ea57b7bd8294e4c9445e
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.
