Guess the PPC mozilla packages were built just doing rpmbuild
--rebuild. So,
<
http://ftp.redhat.com/pub/redhat/linux/rawhide/ppc/Fedora/RPMS/> has
mozilla _PPC_ binary pacakges built with OPTFLAGS=-O2 and CXXFLAGS=-g
(!?!).
After removing these lines from the spec file, that really should
consider other architectures, and doing rpmbuild -bb, I could
successfully build mozilla packages that actually _work_ on PPC.