Move to Xcode 9.3 which also means a High Sierra image.

.travis.yml

@@ -14,21 +14,21 @@ matrix:
 
     - os: osx
       env: CONFIG=objectivec_osx
-      osx_image: xcode9.1
+      osx_image: xcode9.3
       language: objective-c
     # iOS build log was starting to choke travis UI, so split to cover the
     # Xcode Debug and Release Configurations independently.
     - os: osx
       env: CONFIG=objectivec_ios_debug
-      osx_image: xcode9.1
+      osx_image: xcode9.3
       language: objective-c
     - os: osx
       env: CONFIG=objectivec_ios_release
-      osx_image: xcode9.1
+      osx_image: xcode9.3
       language: objective-c
     - os: osx
       env: CONFIG=objectivec_cocoapods_integration
-      osx_image: xcode9.1
+      osx_image: xcode9.3
       language: objective-c
 
     # -----------------------------------------------------------------

objectivec/DevTools/full_mac_build.sh

@@ -269,8 +269,20 @@ if [[ "${DO_XCODE_IOS_TESTS}" == "yes" ]] ; then
           -disable-concurrent-testing
       )
       ;;
+    9.3* )
+      XCODEBUILD_TEST_BASE_IOS+=(
+          # Xcode 9.3 chokes targeting iOS 8.x - http://www.openradar.me/39335367
+          -destination "platform=iOS Simulator,name=iPhone 4s,OS=9.0" # 32bit
+          -destination "platform=iOS Simulator,name=iPhone 7,OS=latest" # 64bit
+          # 9.3 also seems to often fail running destinations in parallel
+          -disable-concurrent-testing
+      )
+      ;;
     * )
-      echo "Time to update the simulator targets for Xcode ${XCODE_VERSION}"
+      echo ""
+      echo "ATTENTION: Time to update the simulator targets for Xcode ${XCODE_VERSION}"
+      echo ""
+      echo "Build aborted!"
       exit 2
       ;;
   esac