It turns out that on some targets we generate a call to initialize a
SIMD vector from a Builtin.Vec, even though everything is transparent,
so the checks for the return using a specific value were too fragile.
rdar://153260158
Older iOS / watchOS targets do not default to having armv8.2 FP16 enabled, so FileCheck was failing when building for those because we didn't have the "right" assembly pattern. Stop testing Float16 compare codegen for now. I'll restore it with an IR test instead of assembly.
Resolves <rdar://152418752>
There's no reason for these to ever be calls, so they should be
transparent instead of just aEIC. Also adds concrete versions of
comparisons with scalars, and filecheck tests to make sure these
generate 1-2 instruction sequences in release on arm64 (x86_64 is a
little trickier to test due to frame pointers, but if we get the right
codgen on arm64, in practice we do well on x86_64 for these too).
Also makes filecheck patterns for repeating initializers a bit more
robust.
