[llvm-branch-commits] [SPIRV] Pass optLevel to InstructionSelect (PR #217929)

[Aiden Grossman via llvm-branch-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/217929

Canonical with all other targets (minus m68k which I will fix next).
Seems to have been dropped in eab7d3639b3c6dc9dda9a0ab1643f0e45ad2d9d6
accidentally when introducing the InstructionSelect subclass to avoid
the need for RegBankSelect.