mac: Update clang build script for the SDK 11.1 bump

The SDK was updated to 11.1 in crrev.com/844553. This updates the build
script to match

Bug: 1168134
Change-Id: Ia9054b5b49e7f24bc9135ccd6024e3c8af8cd518
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2637477
Commit-Queue: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844775}

tools/clang/scripts/build.py

@@ -792,8 +792,8 @@ def main():
         '-DDARWIN_iossim_ARCHS=i386;x86_64;arm64',
     ])
     if args.bootstrap:
-      # mac/arm64 needs MacOSX11.0.sdk. System Xcode (+ SDK) on the chrome bots
-      # is something much older.
+      # mac/arm64 needs MacOSX11.0.sdk. System Xcode (+ SDK) may be something
+      # else, so use the hermetic Xcode.
       # Options:
       # - temporarily set system Xcode to Xcode 12 beta while running this
       #   script, (cf build/swarming_xcode_install.py, but it looks unused)
@@ -805,11 +805,11 @@ def main():
       #   LLVM build without it being system Xcode.
       #
       # The last option seems best, so let's go with that. We need to pass
-      # -isysroot to the 11.0 SDK and -B to the /usr/bin so that the new ld64 is
+      # -isysroot to the SDK and -B to the /usr/bin so that the new ld64 is
       # used.
       # The compiler-rt build overrides -isysroot flags set via cflags, and we
       # only need to use the 11 SDK for the compiler-rt build. So set only
-      # DARWIN_macosx_CACHED_SYSROOT to the 11.0 SDK and use the regular SDK
+      # DARWIN_macosx_CACHED_SYSROOT to the 11 SDK and use the regular SDK
       # for the rest of the build. (The new ld is used for all links.)
       sys.path.insert(1, os.path.join(CHROMIUM_DIR, 'build'))
       import mac_toolchain
@@ -817,12 +817,12 @@ def main():
       mac_toolchain.InstallXcodeBinaries(LLVM_XCODE)
       isysroot_11 = os.path.join(LLVM_XCODE, 'Contents', 'Developer',
                                  'Platforms', 'MacOSX.platform', 'Developer',
-                                 'SDKs', 'MacOSX11.0.sdk')
+                                 'SDKs', 'MacOSX11.1.sdk')
       xcode_bin = os.path.join(LLVM_XCODE, 'Contents', 'Developer',
                                'Toolchains', 'XcodeDefault.xctoolchain', 'usr',
                                'bin')
       # Include an arm64 slice for libclang_rt.osx.a. This requires using
-      # MacOSX11.0.sdk (via -isysroot, via DARWIN_macosx_CACHED_SYSROOT) and
+      # MacOSX11.x.sdk (via -isysroot, via DARWIN_macosx_CACHED_SYSROOT) and
       # the new ld, via -B
       compiler_rt_args.extend([
           # We don't need 32-bit intel support for macOS, we only ship 64-bit.