[3.12] gh-125698: Autoconf: Sync EXEEXT and ac_exeext (GH-125995) (#126007)

(cherry picked from commit 8b7cdc5)

Co-authored-by: Erlend E. Aasland <[email protected]>

Author: miss-islington

configure

@@ -1308,6 +1308,9 @@ AC_ARG_WITH([suffix],
 ])
 AC_MSG_RESULT([$EXEEXT])
 
+# Make sure we keep EXEEXT and ac_exeext sync'ed.
+AS_VAR_SET([ac_exeext], [$EXEEXT])
+
 # Test whether we're running on a non-case-sensitive system, in which
 # case we give a warning if no ext is given
 AC_SUBST([BUILDEXEEXT])