For most of the 2010s, the OpenBSD base system has been stuck with GCC 4.2.1. It was released in July 2007, imported into the OpenBSD source tree in October 2009, and became the default compiler on the amd64, i386, hppa, sparc64, socppc and macppc platforms in OpenBSD 4.8, released in November 2010. As specified in the commit message during import, this is the last version released under the GPLv2 license.
OpenBSD was not the only operating system sticking to GCC 4.2.1 for licensing reasons, FreeBSD did the same, and Mac OS X as well.
As a general rule, and this is not OpenBSD specific, being stuck with old compilers is problematic for several reasons.
It seems most platforms OpenBSD supports now come with modern, up-to-date toolchains.