Hide dup3() and pipe2() from configure on macOS older than 27

The macOS 27 SDK declares both as available since macOS 27.0, and
`AC_CHECK_FUNCS` detects them regardless of the deployment target, so
Ruby built on macOS 26 with the Command Line Tools 27 calls weakly
linked NULL symbols and crashes miniruby during the build.

https://bugs.ruby-lang.org/issues/22311
#2640

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: hsbt

bin/ruby-build

@@ -754,6 +754,13 @@ build_package_standard() {
       # override them and notably lose the -O3, producing a -O0 Ruby.
       export cflags="-std=gnu17 $cflags"
     fi
+    if [ "$package_var_name" = "RUBY" ] && is_mac && ! is_mac 2700; then
+      # The macOS 27 SDK declares dup3() and pipe2() as available since macOS 27.0.
+      # Ruby's configure detects them even when building for an older macOS, where
+      # they are only weakly linked and are NULL at runtime, which makes miniruby
+      # crash during the build: https://bugs.ruby-lang.org/issues/22311
+      export ac_cv_func_dup3=no ac_cv_func_pipe2=no
+    fi
     # ./configure --prefix=/path/to/ruby
     # shellcheck disable=SC2086,SC2153
     capture_command ${!PACKAGE_CONFIGURE:-./configure} --prefix="${!PACKAGE_PREFIX_PATH:-$PREFIX_PATH}" \

test/compiler.bats

@@ -12,7 +12,7 @@ export -n RUBY_CONFIGURE_OPTS
   cd "$INSTALL_ROOT"
 
   stub_repeated uname '-s : echo Darwin'
-  stub sw_vers '-productVersion : echo 10.10'
+  stub_repeated sw_vers '-productVersion : echo 10.10'
   stub_repeated brew 'false'
   # shellcheck disable=SC2016
   stub_repeated make 'echo "make $(inspect_args "$@")" >> build.log'
@@ -43,3 +43,77 @@ OUT
   unstub brew
   unstub make
 }
+
+@test "dup3 and pipe2 are hidden from configure when building on older macOS" {
+  mkdir -p "$INSTALL_ROOT"
+  cd "$INSTALL_ROOT"
+
+  stub_repeated uname '-s : echo Darwin'
+  stub_repeated sw_vers '-productVersion : echo 26.6.2'
+  stub_repeated brew 'false'
+  # shellcheck disable=SC2016
+  stub_repeated make 'echo "make $(inspect_args "$@")" >> build.log'
+
+  cat > ./configure <<CON
+#!${BASH}
+echo ./configure "\$@" > build.log
+echo dup3=\${ac_cv_func_dup3-unset} >> build.log
+echo pipe2=\${ac_cv_func_pipe2-unset} >> build.log
+CON
+  chmod +x ./configure
+
+  run_inline_definition <<DEF
+build_package_standard ruby-3.4.0
+DEF
+  assert_success
+  run cat build.log
+  assert_output <<OUT
+./configure --prefix=$INSTALL_ROOT --with-ext=openssl,psych,+
+dup3=no
+pipe2=no
+make -j 2
+make install
+OUT
+
+  unstub uname
+  unstub sw_vers
+  unstub brew
+  unstub make
+}
+
+@test "dup3 and pipe2 are left to configure on macOS 27" {
+  mkdir -p "$INSTALL_ROOT"
+  cd "$INSTALL_ROOT"
+
+  stub_repeated uname '-s : echo Darwin'
+  stub_repeated sw_vers '-productVersion : echo 27.0'
+  stub_repeated brew 'false'
+  # shellcheck disable=SC2016
+  stub_repeated make 'echo "make $(inspect_args "$@")" >> build.log'
+
+  cat > ./configure <<CON
+#!${BASH}
+echo ./configure "\$@" > build.log
+echo dup3=\${ac_cv_func_dup3-unset} >> build.log
+echo pipe2=\${ac_cv_func_pipe2-unset} >> build.log
+CON
+  chmod +x ./configure
+
+  run_inline_definition <<DEF
+build_package_standard ruby-3.4.0
+DEF
+  assert_success
+  run cat build.log
+  assert_output <<OUT
+./configure --prefix=$INSTALL_ROOT --with-ext=openssl,psych,+
+dup3=unset
+pipe2=unset
+make -j 2
+make install
+OUT
+
+  unstub uname
+  unstub sw_vers
+  unstub brew
+  unstub make
+}