For the record the specific autoconf macro: AC_SEARCH_LIBS([__atomic_load_8],[atomic], ...)
Produces this test code: " | #ifdef __cplusplus | extern "C" | #endif | char __atomic_load_8 (); | int | main () | { | return __atomic_load_8 (); | ; | return 0; | } " Which produces this (on all buildd's including the working ones): " conftest.cpp:56:6: error: new declaration 'char __atomic_load_8()' ambiguates built-in declaration 'long long unsigned int __atomic_load_8(const volatile void*, int)' [-fpermissive] char __atomic_load_8 (); ^~~~~~~~~~~~~~~ conftest.cpp: In function 'int main()': conftest.cpp:60:25: error: too few arguments to function 'long long unsigned int __atomic_load_8(const volatile void*, int)' return __atomic_load_8 (); ^ " "checking for library containing __atomic_load_8... no" Amos