Created attachment 77157 [details]
Mesa uses ffsll, which isn't present on Solaris. It is however present as a builtin in gcc, which is sufficient. But for unclear reasons the Mesa headers will only properly use that on a specific list of platforms, instead of all gcc compliations.
Attached patch removes this restrictive list and uses the builtins whenever gcc is used and the native versions are missing.
For what it's worth Solaris 11 and later have ffsll(), but not older releases.
The patch to use the gcc builtins when possible makes sense to me.
Should be fixed with commit 95df2b28831147b3e7ce2a3b6257bf60c46b4ab4