Similar to 806761a7629df268c8aed49657aeccffa6bca449
-mtriple= specifies the full target triple while -march= merely sets the
architecture part of the default target triple, leaving a target triple which
may not make sense.
Therefore, -march= is error-prone and not recommended for tests without a target
triple. The issue has been benign as we recognize $ve-apple-darwin as ELF instead
of rejecting it outrightly.
Use the `VMRG` for all three operations for now. `vp_select` will be
used in passthru patterns.
Reviewed By: kaz7
Differential Revision: https://reviews.llvm.org/D117206
