This adds the build profiles for ppc64 targets as well as
modifications in other parts of the infra.
These targets are supported:
- ppc64le (glibc little endian elfv2)
- ppc64le-musl (musl little endian)
- ppc64-musl (musl big endian)
ELFv1 targets are explicitly not supported at this point.
Big endian musl supports ppc 970 or newer, while little endian
targets are set to a generic powerpc64le which effectively means
POWER8 and newer. Tuning is always set for POWER9, which is the
most likely target hardware. We also make sure AltiVec is always
on, because it is supported on all hardware we target.
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