Update CI jobs xcode/macOS version to match PyTorch core (#3778)

xcode Version 9 is no longer supported by Apple. https://developer.apple.com/support/xcode/

Updating xcode to 12.0, which also updates the macOS to 10.15.

See https://circleci.com/docs/2.0/testing-ios/#supported-xcode-versions

.circleci/config.yml

@@ -337,7 +337,7 @@ jobs:
   binary_macos_wheel:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout_merge
       - designate_upload_channel
@@ -397,7 +397,7 @@ jobs:
   binary_macos_conda:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout_merge
       - designate_upload_channel
@@ -739,7 +739,7 @@ jobs:
   unittest_macos_cpu:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     resource_class: large
     steps:
       - checkout
@@ -815,7 +815,7 @@ jobs:
   cmake_macos_cpu:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout_merge
       - designate_upload_channel

.circleci/config.yml.in

@@ -337,7 +337,7 @@ jobs:
   binary_macos_wheel:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout_merge
       - designate_upload_channel
@@ -397,7 +397,7 @@ jobs:
   binary_macos_conda:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout_merge
       - designate_upload_channel
@@ -739,7 +739,7 @@ jobs:
   unittest_macos_cpu:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     resource_class: large
     steps:
       - checkout
@@ -815,7 +815,7 @@ jobs:
   cmake_macos_cpu:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout_merge
       - designate_upload_channel