For the case where there is no stdatomic.h header but Atomic works, does it still build fine without including the header?

If so, then we could just do this:

diff --git a/lib/easy_lock.h b/lib/easy_lock.h
index 07c85c5ff..174c0222c 100644
--- a/lib/easy_lock.h
+++ b/lib/easy_lock.h
@@ -33,11 +33,13 @@
 
 #define curl_simple_lock_lock(m) AcquireSRWLockExclusive(m)
 #define curl_simple_lock_unlock(m) ReleaseSRWLockExclusive(m)
 
 #elif defined (HAVE_ATOMIC)
+#ifdef HAVE_STDATOMIC_H
 #include <stdatomic.h>
+#endif
 #if defined(HAVE_SCHED_YIELD)
 #include <sched.h>
 #endif
 
 #define curl_simple_lock atomic_bool
diff --git a/m4/curl-functions.m4 b/m4/curl-functions.m4
index ec406f56a..80bc4ca3c 100644
--- a/m4/curl-functions.m4
+++ b/m4/curl-functions.m4
@@ -6584,10 +6584,11 @@ AC_DEFUN([CURL_ATOMIC],[
   ],[
     AC_MSG_RESULT([yes])
     AC_DEFINE_UNQUOTED(HAVE_ATOMIC, 1,
       [Define to 1 if you have _Atomic support.])
     tst_atomic="yes"
+    AC_CHECK_HEADERS(stdatomic.h)
   ],[
     AC_MSG_RESULT([no])
     tst_atomic="no"
   ])
 ])

I suppose it's not likely to work without the header since we use atomic_bool in the code but check for _Atomic in configure... Let me do a proper PR instead.

Yeah, _Atomic is a language keyword and so its existence is just dependent on the compiler, whereas the typedefs for atomic_bool etc. are in stdatomic.h.

yeah, I figured that out as well, so in the #9060 PR, configure will only set HAVE_ATOMIC if both the header is present and the type check works.

I have tried building libCurl 7.84.0 in AIX 7.2 using XLC 16.1.0 , but we facing issue, while running gmake:

In file included from easy.c:89:
../lib/easy_lock.h:38:10: fatal error: 'stdatomic.h' file not found

while in configure step we saw: checking if _Atomic is available... yes

I tried with the fix provided in #9060
But that is also not working.

@Vibhanshu09 can you please try the current git master, and if that still doesn't work file a new issue for your case?

Thank you for the help. I tried with latest main branch, which is working fine. Can you please provide me Estimated date for official release of 7.85.0.