[llvm] [ValueTracking] Improve `Bitcast` handling to match SDAG (PR #125935)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

FWIW, the miscompile can be reproduced with https://martin.st/temp/loopfilter_sse2-preproc.c - compiled as `clang -target x86_64-linux-gnu -O3 -std=gnu99 loopfilter_sse2-preproc.c -c`.

https://github.com/llvm/llvm-project/pull/125935