[llvm] Fix parentheses for clarity in X86ISelLowering.cpp (PR #121954)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

Have you been able to work through "[Getting the Source Code and Building LLVM](https://llvm.org/docs/GettingStarted.html#id4)" section?

I'd recommend using something like: `cmake -S llvm -B build -G Ninja -DCMAKE_C_FLAGS='-Wall -Wextra' -DCMAKE_CXX_FLAGS='-Wall -Wextra' -DLLVM_TARGETS_TO_BUILD="X86"` to just build the X86 target

https://github.com/llvm/llvm-project/pull/121954