powerpc: Pre-load long constants & invariants

PowerPC doesn't have an easy way to load a long constant into a
vector register so we emit the value into the code and then load it.

This moves those values to after the epilogue and then loads them
before starting the outer loop.
5 jobs for misc in 2 minutes and 4 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #582002
debian sid

00:00:45

passed #581979
docker windows 1607
msys2

00:01:15

passed #581977
docker windows 1607
vs2017 amd64

00:01:18

passed #581978
docker windows 1607
vs2017 x86

00:01:18

failed #581976
debian sid

00:02:00