Generally speaking, follow the Linux Build Instructions. However, do the following instead to install the build dependencies:
Most of these packages are probably already installed since they're often used, and the --needed parameter ensures that up-to-date packages are not reinstalled.
$ sudo pacman -S --needed python perl gcc gcc-libs bison flex gperf pkgconfig \ nss alsa-lib gconf glib2 gtk2 nspr ttf-ms-fonts freetype2 cairo dbus \ libgnome-keyring
For the optional packages on Arch Linux:
php-cgi is provided with pacmanwdiff is not in the main repository but dwdiff is. You can get wdiff in AUR/yaourtsun-java6-fonts do not seem to be in main repository or AUR.