> If we want to respect sizeof(max_align_t) alignment, we can compute sizeof(max_align_t) in configure and uses the result in obmalloc.c. I expect that it's either 16 or 32, so we can maybe just hardcode ALIGNMENT_SHIFT using something like: "if == 32 ... #elif == 16 ... #else #error ...".

This should be "alignof(max_align_t)" instead of "sizeof(...)". The size itself is not relevant.

BTW, on macOS/arm64 alignof(max_align_t) is 8, not 16 (as the code seems to expect given the pointer size). This is harmless of course.