[clang] [clang][bytecode] Check for integral types in evaluateStrlen (PR #185481)

[Timm Baeder via cfe-commits]

tbaederr wrote:

> The fact that this PR is necessary seems to point to the current name resulting in it being used incorrectly.

How does that make sense? This PR is necessary because there was _no_ such check before, not because there was the wrong check.

Let me check where fixed point types are needed in `isIntegralType()`.

https://github.com/llvm/llvm-project/pull/185481