Reland https://github.com/llvm/llvm-project/pull/108985
Extend `LoopIdiomRecognize` to find and replace loops of the form
```c
base = str;
while (*str)
++str;
```
and transforming the `strlen` loop idiom into the appropriate `strlen`
and `wcslen` library call which will give a small performance boost if
replaced.
```c
str = base + strlen(base)
len = str - base
```
9694844d7e