Note: We aren't removing 970 (aka G5) support, only server POWER4.
Be advised that I have gone in very big circles with gcc 7.3.0 and the
test variants for gcc 8 on an old IBM 970 Power ISA v.2.03 spec G5 unit.
Some weird things happen if one tries various options on the GCC manual
for "IBM RS/6000 and PowerPC Options" wherein you may get either the
IBM long double or the IEEE 754-2008 long double and strange results
then follow.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85440
I would suggest that the old 970 won't function as expected for much
longer and the IBM Power architecture seems to be where efforts are
focused. The glibc releases for 2.26 and 2.27 were clear on this.
The older things called "powerpc" or just previous to Power ISA v.2.05
are falling into the category that I call "historical artifacts" much
like the old DEC Alpha.
Dennis