Merge pull request #3182 from ilovezfs/ac_cv_xcode9

superenv: help Autotools with 10.13 SDK on 10.12

Author: ilovezfs

Library/Homebrew/extend/os/mac/extend/ENV/super.rb

@@ -96,9 +96,12 @@ def setup_build_environment(formula = nil)
       self["SDKROOT"] = MacOS.sdk_path
     end
 
-    # Filter out symbols known not to be defined on 10.11 since GNU Autotools
-    # can't reliably figure this out with Xcode 8 on its own yet.
-    if MacOS.version == "10.11" && MacOS::Xcode.installed? && MacOS::Xcode.version >= "8.0"
+    # Filter out symbols known not to be defined since GNU Autotools can't
+    # reliably figure this out with Xcode 8 and above.
+    if MacOS.version == "10.12" && MacOS::Xcode.installed? && MacOS::Xcode.version >= "9.0"
+      ENV["ac_cv_func_futimens"] = "no"
+      ENV["ac_cv_func_utimensat"] = "no"
+    elsif MacOS.version == "10.11" && MacOS::Xcode.installed? && MacOS::Xcode.version >= "8.0"
       %w[basename_r clock_getres clock_gettime clock_settime dirname_r
          getentropy mkostemp mkostemps timingsafe_bcmp].each do |s|
         ENV["ac_cv_func_#{s}"] = "no"