> I can't find anything that is providing a non-empty definition of > PG_USED_FOR_ASSERTS_ONLY (a/k/a pg_attribute_unused) for anything > except GCC.
It's supported in clang as well per the documentation [0] in at least some configurations or distributions:
"The [[maybe_unused]] (or __attribute__((unused))) attribute can be used to silence such diagnostics when the entity cannot be removed. For instance, a local variable may exist solely for use in an assert() statement, which makes the local variable unused when NDEBUG is defined."
[[maybe_unused]] is also recognized from Visual Studio 2017 onwards [1].