Turns out that the instrumentation added for gcov can change inlining
decisions of the compiler, which results in a mismatch between the
profile data CFG and the actual generated CFG between compiles.
There are two functions that suffer from this issue:
1. _PHP_XXH3_Init: Removing the inline hint fixes this one. In fact,
always inlining this makes no sense as there's no real opportunity
for specialising. It just bloats the binary and increases I$ pressure.
So besides fixing this issue it's beneficial on its own to drop the
attribute.
2. PHP_XXH3_128_Final: Sometimes XXH128_canonicalFromHash gets inlined
and sometimes not. Make sure it gets always inlined.
Closes GH-18814.
afb1c57470