[llvm] [X86] Avoid shl->mul lowbit-isolate fold when BMI1/BMI2 are available (PR #217776)

[PJ Dailey via llvm-commits]

PjDailey11 wrote:

> Using a BMI1/BMI2 check will still improperly apply this fold to bdver2, bdver3, and btver2 because they don't have BMI2 but would still prefer TZCNT. It might be better to check only BMI1 because Intel didn't make CPUs with only BMI1 like AMD.

Okay, just checked `bdver2`/`bdver3`/`btver2` and saw they have `BMI1`. I understand because the only reason to have `BMI2` was to have `SHLX`. I will switch it to `hasBMI()` instead

https://github.com/llvm/llvm-project/pull/217776