IRIX has been obsolete for years now, but the hardware is still interesting to me. Here's some stuff I've managed to build.
DISCLAIMER: This software works on my machine. I can't guarantee anything else, but it actually does work on my machine. For a smooth experience, I suggest using Nekoware gcc or MIPSpro for now.
Cross-built on a Linux host. Includes GNU binutils 2.17.
This is an updated version, fixing a couple of stupidities in the previous tarball. After installing it, edit /opt/local/gcc-4.7.4/libexec/gcc/mips-sgi-irix6.5/4.7.4/install-tools/mkheaders to point to your copy of bash (it appears in three places in the file) and run the script to get fixed versions of headers in /opt/local/gcc-4.7.4/lib/gcc/mips-sgi-irix6.5/4.7.4/include-fixed.
This one supports -r option, making it rather useful for finding out where something is #defined.
Inside the file there is an optlocal.profile file which sets rld search paths accordingly.
NOTE: this includes an /etc/sudoers file with my username. Replace with yours instead of blaming me about trying to hack you.
NOTE: curl expects to find a cacert.pem containing certificates in /opt/local/etc. More info.
This is a constantly updated document describing my adventures with pkgsrc on IRIX in 2018.