I am following the August 30 version of "Gentoo Linux GCC Upgrade Guide". My system is a fairly recently prepared stage3 installation with gcc-3.4.6 prior to the upgrade. I have kept the portage tree synced and done `emerge --system' updates now and then (and `etc-update' as needed). After an `emerge --sync' today (September 1) I started out doing `emerge -uav gcc' as the guide says. This resulted in 4 packages being emerged: number 3 was gcc-4.1.1 and number 4 was glibc-2.4-r3. The emerge of glibc however came to an early halt, telling me to declare USE="nptl nptlonly". I did so in /etc/make.conf and re-launched the emerge command, which is now hopefully doing fine (it is cranking along since over an hour). My point then: The Guide should tell about the need for the USE flags. Especially so since the stoppage occurs in the middle of a command that runs for hours (on old Pentium-III hardware at least). And, I suppose that the advice has to be conditional: It applies when going from gcc 3 to ggc 4, but not necessarily to other gcc upgrades.
That guide is specifically for GCC, _not_ glibc. Anyway, seems that glibc has had this functionality for quite some time... That's why you should always run emerge -pvt [package] before updating. :)
It is a gcc guide only, but following the instructions (emerge -uav gcc specifically) causes glibc to be installed, and to fail. Anything which the instructions cause to fail should be described in the guide. Also, since there is this gcc/glibc changeover, the glibc use flags should be mentioned somewhere that everyone is pointed to. The only place for that, currently, is the gcc upgrade guide.
