[llvm] TargetLibraryInfo: Use pointer index size to determine getSizeTSize(). (PR #118747)

[Owen Anderson via llvm-commits]

resistor wrote:

Tagging @nzaghen specifically because of the changes in `stdio-custom-dl.ll`. The file was added by them in https://reviews.llvm.org/D68328

It's clear that the file is intended to test the opposite of the behavior being implemented here, but the reasoning behind that expectation is not clear to me.

https://github.com/llvm/llvm-project/pull/118747