gh-153711: Avoid use of dup3 and pipe2 calls introduced in macOS 27

This prevents potential segfaults when builds are used on older
systems and avoids adding new code for supporting weaklinking.

Author: ned-deily

Misc/NEWS.d/next/macOS/2026-08-05-02-02-33.gh-issue-153711.pO9fFb.rst

@@ -0,0 +1,2 @@
+Do not attempt to use the `dup3` and `pipe2` system calls introduced in
+macOS 27 to prevent problems when running on older systems.

configure

@@ -5361,7 +5361,13 @@ fi
 # header definition prevents usage - autoconf doesn't use the headers), or
 # raise an error if used at runtime. Force these symbols off.
 if test "$ac_sys_system" != "iOS" ; then
-  AC_CHECK_FUNCS([dup3 getentropy getgroups pipe2 system])
+  AC_CHECK_FUNCS([getentropy getgroups system])
+fi
+# In addition, macOS introduced dup3 and pipe2 in macOS 27, late in the
+# lifetime of this version of Python. Rather than adding weaklinking
+# support for them, just continue to ignore them.
+if test "$ac_sys_system" != "iOS" -a "$ac_sys_system" != "Darwin"; then
+  AC_CHECK_FUNCS([dup3 pipe2])
 fi
 
 AC_CHECK_DECL([dirfd],