[llvm] [RegAlloc] Remove default restriction on non-trivial rematerialization (PR #159211)

[Luke Lau via llvm-commits]

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lukel97 wrote:

Because this now gets rematerialized we need another way of showing that the register pressure is too high, so I copied what was originally done in https://reviews.llvm.org/D106408 to convert it to an MIR test.

https://github.com/llvm/llvm-project/pull/159211