Ensure Bazel uses the correct Xcode version when compiling

This is three changes:
- On the command-line, set `--xcode_version` to whatever `xcode-select` is set to
- In Xcode, set `--xcode_version` to `$XCODE_PRODUCT_BUILD_VERSION`
- For both, set `--repo_env=USE_CLANG_CL= $XCODE_PRODUCT_BUILD_VERSION` to work around bazelbuild/bazel#8902

Author: brentleyjones

examples/cc/test/fixtures/bwb.xcodeproj/rules_xcodeproj/bazel/bazel_build.sh

@@ -89,6 +89,15 @@ bazel_cmd=(
   "$BAZEL_PATH"
   "${bazelrcs[@]}"
 )
+pre_config_flags=(
+  # Be explicit about our desired Xcode version
+  "--xcode_version=$XCODE_PRODUCT_BUILD_VERSION"
+
+  # Work around https://github.com/bazelbuild/bazel/issues/8902
+  # `USE_CLANG_CL` is only used on Windows, we set it here to cause Bazel to
+  # re-evaluate the cc_toolchain for a different Xcode version
+  "--repo_env=USE_CLANG_CL=$XCODE_PRODUCT_BUILD_VERSION"
+)
 
 # Determine Bazel output_path
 
@@ -111,7 +120,11 @@ else
 fi
 
 output_path=$("${bazel_cmd[@]}" \
-  info --config="${BAZEL_CONFIG}_info" --color="$color" output_path)
+  info \
+  "${pre_config_flags[@]}" \
+  --config="${BAZEL_CONFIG}_info" \
+  --color="$color" \
+  output_path)
 execution_root="${output_path%/*}"
 
 # Create `bazel.lldbinit``
@@ -181,6 +194,7 @@ touch "$build_marker"
 "$BAZEL_INTEGRATION_DIR/process_bazel_build_log.py" \
   "${bazel_cmd[@]}" \
   build \
+  "${pre_config_flags[@]}" \
   --config="$config" \
   --color=yes \
   ${toolchain:+--define=SWIFT_CUSTOM_TOOLCHAIN="$toolchain"} \

examples/cc/test/fixtures/bwx.xcodeproj/rules_xcodeproj/bazel/bazel_build.sh

@@ -52,6 +52,17 @@ if [[ -s "$extra_flags_bazelrc" ]]; then
   bazelrcs+=("--bazelrc=$extra_flags_bazelrc")
 fi
 
+xcode_build_version=$(/usr/bin/xcodebuild -version | tail -1 | cut -d " " -f3)
+pre_config_flags=(
+  # Be explicit about our desired Xcode version
+  "--xcode_version=$xcode_build_version"
+
+  # Work around https://github.com/bazelbuild/bazel/issues/8902
+  # `USE_CLANG_CL` is only used on Windows, we set it here to cause Bazel to
+  # re-evaluate the cc_toolchain for a different Xcode version
+  "--repo_env=USE_CLANG_CL=$xcode_build_version"
+)
+
 # Ensure that our top-level cache buster `new_local_repository` is valid
 mkdir -p /tmp/rules_xcodeproj
 date +%s > "/tmp/rules_xcodeproj/top_level_cache_buster"
@@ -63,6 +74,7 @@ if [[ -z "${build_output_groups:-}" ]]; then
   "%bazel_path%" \
     "${bazelrcs[@]}" \
     run \
+    "${pre_config_flags[@]}" \
     "--config=%config%_generator" \
     %extra_generator_flags% \
     "%generator_label%" \
@@ -73,6 +85,7 @@ else
   "%bazel_path%" \
     "${bazelrcs[@]}" \
     build \
+    "${pre_config_flags[@]}" \
     "--config=_%config%_build" \
     --output_groups="$build_output_groups" \
     "%generator_label%"