Bring back XCode selection CI script

This reverts commit 8514b0097b.

.github/workflows/ci.yml

@@ -96,6 +96,9 @@ jobs:
       - name: install sccache
         run: src/ci/scripts/install-sccache.sh
         if: success() && !env.SKIP_JOB
+      - name: select Xcode
+        run: src/ci/scripts/select-xcode.sh
+        if: success() && !env.SKIP_JOB
       - name: install clang
         run: src/ci/scripts/install-clang.sh
         if: success() && !env.SKIP_JOB
@@ -353,6 +356,7 @@ jobs:
               SCRIPT: "./x.py dist bootstrap --include-default-paths --stage 2"
               RUST_CONFIGURE_ARGS: "--build=x86_64-apple-darwin --host=aarch64-apple-darwin --target=aarch64-apple-darwin --enable-full-tools --enable-sanitizers --enable-profiler --disable-docs --set rust.jemalloc --set llvm.ninja=false"
               RUSTC_RETRY_LINKER_ON_SEGFAULT: 1
+              SELECT_XCODE: /Applications/Xcode_12.2.app
               USE_XCODE_CLANG: 1
               MACOSX_DEPLOYMENT_TARGET: 11.0
               MACOSX_STD_DEPLOYMENT_TARGET: 11.0
@@ -503,6 +507,9 @@ jobs:
       - name: install sccache
         run: src/ci/scripts/install-sccache.sh
         if: success() && !env.SKIP_JOB
+      - name: select Xcode
+        run: src/ci/scripts/select-xcode.sh
+        if: success() && !env.SKIP_JOB
       - name: install clang
         run: src/ci/scripts/install-clang.sh
         if: success() && !env.SKIP_JOB
@@ -615,6 +622,9 @@ jobs:
       - name: install sccache
         run: src/ci/scripts/install-sccache.sh
         if: success() && !env.SKIP_JOB
+      - name: select Xcode
+        run: src/ci/scripts/select-xcode.sh
+        if: success() && !env.SKIP_JOB
       - name: install clang
         run: src/ci/scripts/install-clang.sh
         if: success() && !env.SKIP_JOB

src/ci/github-actions/ci.yml

@@ -153,6 +153,10 @@ x--expand-yaml-anchors--remove:
         run: src/ci/scripts/install-sccache.sh
         <<: *step
 
+      - name: select Xcode
+        run: src/ci/scripts/select-xcode.sh
+        <<: *step
+
       - name: install clang
         run: src/ci/scripts/install-clang.sh
         <<: *step
@@ -527,6 +531,7 @@ jobs:
                 --set rust.jemalloc
                 --set llvm.ninja=false
               RUSTC_RETRY_LINKER_ON_SEGFAULT: 1
+              SELECT_XCODE: /Applications/Xcode_12.2.app
               USE_XCODE_CLANG: 1
               MACOSX_DEPLOYMENT_TARGET: 11.0
               MACOSX_STD_DEPLOYMENT_TARGET: 11.0

src/ci/scripts/select-xcode.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+# This script selects the Xcode instance to use.
+
+set -euo pipefail
+IFS=$'\n\t'
+
+source "$(cd "$(dirname "$0")" && pwd)/../shared.sh"
+
+if isMacOS; then
+    if [[ -s "${SELECT_XCODE-}" ]]; then
+        sudo xcode-select -s "${SELECT_XCODE}"
+    fi
+fi