Unbreak this port on powerpc64/12 after r561520 updated GCC_DEFAULT
from 9 to 10.

Although this port was tested with GCC 10 on amd64, it was _not_ on
powerpc64, and it seems that GCC10/powerpc64 regresses in several cases
vs. GCC9/powerpc64.

Approved by: portmgr (tier-2 blanket)