[llvm] [GlobalISel][ARM] Selection of G_CONSTANT using constant pool (PR #96225)

[Matt Arsenault via llvm-commits]

arsenm wrote:

You can custom lower, check the value and then use the LegalizerHelper lower implementation if you need to expand it. Alternatively, we can make the default lower implementation for constant check the isImmLegal or whatever it's called TargetLowering hook 

https://github.com/llvm/llvm-project/pull/96225