Narrow test to skip dup3 and pipe2 for iOS 26 and earlier

Author: ned-deily

configure

@@ -439,7 +439,7 @@ if test -z "$AR"; then
 		aarch64-apple-ios*)           AR=arm64-apple-ios-ar ;;
 		x86_64-apple-ios*-simulator)  AR=x86_64-apple-ios-simulator-ar ;;
 		*)
-	esac
+    esac
 fi
 if test -z "$CC"; then
 	case "$host" in
@@ -5576,9 +5576,24 @@ fi
 # found by configure), but either raise a compilation error (because the
 # header definition prevents usage - autoconf doesn't use the headers), or
 # raise an error if used at runtime. Force these symbols off.
-if test "$ac_sys_system" != "iOS" ; then
-  AC_CHECK_FUNCS([getentropy getgroups system])
-fi
+# In particular, dup3 and pipe2 are available as of iOS 27 but were
+# incorrectly detected in older simulator versions.
+case "$ac_sys_system" in
+    iOS)
+        AC_MSG_CHECKING([if iOS SDK is older than 27])
+        ios_sdk_version=$(xcrun --sdk iphoneos --show-sdk-version 2>/dev/null | cut -d. -f1)
+        if test -n "$ios_sdk_version" && test "$ios_sdk_version" -ge 27; then
+            AC_MSG_RESULT([no])
+            AC_CHECK_FUNCS([dup3 pipe2])
+        else
+            AC_MSG_RESULT([yes])
+        fi
+        ;;
+    *)
+        # not iOS
+        AC_CHECK_FUNCS([dup3 getentropy getgroups pipe2 system])
+        ;;
+esac
 
 AC_CHECK_DECL([dirfd],
               [AC_DEFINE([HAVE_DIRFD], [1],
@@ -5590,9 +5605,7 @@ AC_CHECK_DECL([dirfd],
 # For some functions, having a definition is not sufficient, since
 # we want to take their address.
 PY_CHECK_FUNC([chroot], [@%:@include <unistd.h>])
-PY_CHECK_FUNC([dup3], [@%:@include <unistd.h>])
 PY_CHECK_FUNC([link], [@%:@include <unistd.h>])
-PY_CHECK_FUNC([pipe2], [@%:@include <unistd.h>])
 PY_CHECK_FUNC([symlink], [@%:@include <unistd.h>])
 PY_CHECK_FUNC([fchdir], [@%:@include <unistd.h>])
 PY_CHECK_FUNC([fsync], [@%:@include <unistd.h>])

configure.ac

@@ -392,7 +392,7 @@
 /* Define to 1 if you have the 'dup2' function. */
 #undef HAVE_DUP2
 
-/* Define if you have the 'dup3' function. */
+/* Define to 1 if you have the 'dup3' function. */
 #undef HAVE_DUP3
 
 /* Define if you have the '_dyld_shared_cache_contains_path' function. */
@@ -1052,7 +1052,7 @@
 /* Define to 1 if you have the 'pipe' function. */
 #undef HAVE_PIPE
 
-/* Define if you have the 'pipe2' function. */
+/* Define to 1 if you have the 'pipe2' function. */
 #undef HAVE_PIPE2
 
 /* Define to 1 if you have the 'plock' function. */