Ok, I believe I can confirm smoki's findings that only 32 bit kernels are
affected while identically configured 64 bit ones are not.

I'm on Gentoo Linux where I've custom-compiled my whole system, including the
kernel (which, originally, was a 32 bit one). I now took my kernel config and
changed only two things: I turned on the option to compile a 64 bit kernel as
well as the option that allows me to run 32 bit binaries with the resulting
kernel. I then compiled the exact same kernel sources I had used before and
upon booting the new 64 bit kernel Mesa worked absolutely fine without any
visible corruption.

I guess that proves Michels point that this issue seems to be 32 bit toolchain
related.