Without pixman renderer override pgo builds in cage/sway require
access to actual render devices. In Gentoo's case the builds are run
as ordinary user and within a "sandbox" which prevents and logs access
outside of predefined places during build.
So let's default to pixman renderer for the PGO builds. Hopefully that
won't matter for the pgo optimizations to do the right thing within foot.
Appears to work, but cage spams a lot of
00:00:08.026 [types/wlr_output.c:720] Basic output test failed for HEADLESS-1
00:00:08.036 [types/wlr_output.c:720] Basic output test failed for HEADLESS-1
