[clang] [clang] improve consistency with GCC vector comparison (PR #148954)

[Imple Lee via cfe-commits]

ImpleLee wrote:

Now I make a utility function `getGCCCompatibleIntTypeForBitwidth` for this type preference. It should also be used for `mode` attribute.

There is currently no test about this, but I don't know how to or even whether should I write relevant tests.

There are many other places in clang that uses `ASTContext::getIntTypeForBitwidth` or `TargetInfo::getIntTypeByWidth`, but I don't know whether any of them should switch to this function.

https://github.com/llvm/llvm-project/pull/148954