Downgrading packages in Arch Linux

On occasion (actually today was the first time) there is need to downgrade a package in Arch Linux. Yesterday I did a `pacman -Syu`, which upgraded gcc from 4.4.3 to 4.5.0. Today, I learned that 4.5.0 is unable to compile Moab. You'd think that a new release of your trusty compiler would work at least as good as the last one, but that's a topic (spelled R-A-N-T) for another day. When this catastrophe strikes, you can do the following to recover.

1. On my Arch system, package files are kept in /var/cache/pacman/pkg. Go there.

2. Find the desired package. In this particular case, /var/log/pacman.log told me that yesterday I upgraded from 4.4.3-2 to 4.5.0-1. So my working compiler up until yesterday was gcc 4.4.3.

3. "Upgrade" to the desired package: `pacman -U gcc-4.4.3-2-x86_64.pkg.tar.xz` and `pacman -U gcc-libs-4.4.3-2-x86_64.pkg.tar.xz`

4. Also in my case I'll want to stick with gcc 4.4.3 for a while now, so you can modify the IgnorePkg line in /etc/pacman.conf as follows:

IgnorePkg = gcc gcc-libs

This causes pacman to skip over gcc and gcc-libs when you do a system-wide upgrade (mine prints a warning to say it's being ignored, which I don't consider to be a bad thing).