This is because it uses exec_prefix variable from atspi2 pkg-config file to try to find the executables, but atspi2 pkg-config file doesn't have a exec_prefix variable anymore. It was always set to $prefix, so we can just use prefix varaible instead.
Created attachment 435409 [details] Patch
Committed r280965 (240471@main): <https://commits.webkit.org/240471@main>
<rdar://problem/81846671>