Changes

[Legalize][X86] Improve nnan fmin/fmax vector reduction

Use +/-Inf or +/-Largest as neutral element for nnan fmin/fmax
reductions. This avoids dropping any FMF flags. Preserving the
nnan flag in particular is important to get a good lowering on X86.

Differential Revision: https://reviews.llvm.org/D87586

[AArch64][GlobalISel] Promote scalar G_SHL constant shift amounts to s64.

This was supposed to be done in the first place as is currently the case for
G_ASHR and G_LSHR but was forgotten when the original shift legalization
overhaul was done last year.

This was exposed because we started falling back on s32 = s32, s64 SHLs
due to a recent combiner change.

Gives a very minor (0.1%) code size -O0 improvement on consumer-typeset.

Fix MIPS and MIPS64 ABI to use ConstString in their register info arrays.

RegInfoBasedABI::GetRegisterInfoByName was failing because mips/mips64 ABIs
don't use ConstString in their register info array.

Reviewed By: #lldb, teemperor

Differential Revision: https://reviews.llvm.org/D88375

[llvm-objcopy][NFC] refactor error handling. part 2.

Remove usages of special error reporting functions(error(),
reportError()). This patch is extracted from D87987.
Errors are reported as Expected<>/Error returning values.
This part is for COFF subfolder of llvm-objcopy.

Testing: check-all.

Differential Revision: https://reviews.llvm.org/D88213