Robert P. J. DAY says:

According to Mike Frysinger, this patch was removed from Gentoo in the
2.3.x series and didn't seem to cause any adverse effects. So toss it
from the patch directories for glibc 2.5 and up.

 # Compute x86_64-specific values

 CT_DoArchValues() {

     # The architecture part of the tuple:

     CT_TARGET_ARCH="${CT_ARCH}"

 }