Update Xcode to 26.6

[madsmtm]

Update Xcode from 26.2 to 26.6 (released 25 Jun 2026).

This fixes #161561 (at least once Miri updates to the rustc built after this), it seems that Xcode 26.3 and lower's Clang inserts +zcm,+zcz LLVM target features, which newer Clang doesn't like. By building tikv-jemalloc-sys in the sysroot with the newer Xcode/Clang, we avoid the warning.

See this Zulip thread for investigation.

See #152013 for further details on the effects that updating the Xcode version has.

r? shepmaster

[rustbot]

Warning

If you are changing how CI LLVM is built or linked, make sure to bump
src/bootstrap/download-ci-llvm-stamp.

cc @jieyouxu

[madsmtm]

@bors try jobs=apple

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

   Compiling quote v1.0.47
   Compiling serde_core v1.0.229
error: linking with `cc` failed: exit status: 1
  |
  = note:  "cc" "/Users/runner/work/rust/rust/src/ci/citool/../../../build/citool/debug/build/proc-macro2-4417142953ca1d09/rustc7MndK2/symbols.o" "<2 object files omitted>" "<sysroot>/lib/rustlib/aarch64-apple-darwin/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,libcfg_if-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,liblibc-*,librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "-lSystem" "-lc" "-lm" "-arch" "arm64" "-mmacosx-version-min=11.0.0" "-o" "/Users/runner/work/rust/rust/src/ci/citool/../../../build/citool/debug/build/proc-macro2-4417142953ca1d09/build_script_build-4417142953ca1d09" "-Wl,-dead_strip" "-nodefaultlibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: xcrun: error: missing DEVELOPER_DIR path: /Applications/Xcode_26.6.app/Contents/Developer
          

error: linking with `cc` failed: exit status: 1
  |
  = note:  "cc" "/Users/runner/work/rust/rust/src/ci/citool/../../../build/citool/debug/build/quote-410982f58b086895/rustckXmZP6/symbols.o" "<2 object files omitted>" "<sysroot>/lib/rustlib/aarch64-apple-darwin/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,libcfg_if-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,liblibc-*,librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "-lSystem" "-lc" "-lm" "-arch" "arm64" "-mmacosx-version-min=11.0.0" "-o" "/Users/runner/work/rust/rust/src/ci/citool/../../../build/citool/debug/build/quote-410982f58b086895/build_script_build-410982f58b086895" "-Wl,-dead_strip" "-nodefaultlibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: xcrun: error: missing DEVELOPER_DIR path: /Applications/Xcode_26.6.app/Contents/Developer
          

error: linking with `cc` failed: exit status: 1
  |
  = note:  "cc" "/Users/runner/work/rust/rust/src/ci/citool/../../../build/citool/debug/build/serde_core-923d5bcb85e44581/rustcS1jdMS/symbols.o" "<2 object files omitted>" "<sysroot>/lib/rustlib/aarch64-apple-darwin/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,libcfg_if-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,liblibc-*,librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "-lSystem" "-lc" "-lm" "-arch" "arm64" "-mmacosx-version-min=11.0.0" "-o" "/Users/runner/work/rust/rust/src/ci/citool/../../../build/citool/debug/build/serde_core-923d5bcb85e44581/build_script_build-923d5bcb85e44581" "-Wl,-dead_strip" "-nodefaultlibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: xcrun: error: missing DEVELOPER_DIR path: /Applications/Xcode_26.6.app/Contents/Developer
          

error: could not compile `serde_core` (build script) due to 1 previous error

[madsmtm]

Hmm, the macos-15 only installs up to Xcode 26.3, so we have to use the macos-26 image, which is a WIP, see #157687.

[rust-bors]

💔 Test for 3b447a8 failed: CI. Failed jobs:

• try - aarch64-apple-1 (web logs, enhanced plaintext logs)
• try - aarch64-apple-2 (web logs, enhanced plaintext logs)
• try - dist-aarch64-apple (web logs, enhanced plaintext logs)
• try - dist-apple-various (web logs, enhanced plaintext logs)
• try - dist-x86_64-apple (web logs, enhanced plaintext logs)

[rust-bors]

☔ The latest upstream changes (presumably #162035) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.