Iain has sorted out what the error is. Apparently it is fixed in gcc9+, so I'll try those and see if they build i386 now.
He is prepared to backport the fixes into gcc5 to gcc8 so that the i386 builds won't error out if clang/llvm is used as assembler. So once that is available, we can add that, and then we don't have to avoid having clang5+ installed to build gcc any longer on i386 machines. Until that is done and available, gcc5 to 8 at least will not build unless clang5+ is deactivated. Pretty generous of him to use his time like that, to be honest, to support MacPorts. Although it is a bugfix, the chances of anyone else running across this issue outside MacPorts seems pretty unlikely... K
