I saw something about this either here or on Macport Trac a while back so decided to keep two separate install bases: gcc7 on my iBook and gcc11 on the Powerbook. I use the iBook as my buildbox so everything in the repo should be against gcc7 and libgcc7 (except [lib]gcc11 port). There was a small amount of time before I realized this was an issue where libgcc7 was coexisting with libgcc11 on the Powerbok...I don't know if that messed things up or not to be honest. I haven't noticed any problems, but then again I don't use all the software all the time.
Will let you know if I have problems with boost181.
Well, using libgcc7 (i.e. just default settings as they are in the base) will make life easier for the time-being.
Notice, it likely implies that ppc64 is broken – but for G4 that is not a concern. (If anyone wonders – ICU did not build with gcc7 for ppc64, the bug was fixed in gcc10, I guess, and no one backported the fix.)
Mixing will be a bad idea. I recommend staying with gcc7/libgcc7 for 10.4/10.5.8 on 32-bit, or otherwise moving everything to gcc12/libgcc12 (following my PR).
gcc10-bootstrap is immune to the issue, it uses its own libraries.
gcc11 will be broken, unless everything is moved to a newer runtime – or if it is not explicitly broken, it will potentially set one up for a nightmare anyway.