Add '--macos_cpus' option to 'build_qt.py'

This is a preparation to support universal binaries for macOS (#801).

With this commit, you can start building Qt6 as universal binaries as follows.

 # Build universal binaries
 python3 build_tools/build_qt.py --release --confirm_license  \
                                 --macos_cpus=x86_64,arm64

Under the hood, '-DCMAKE_OSX_ARCHITECTURES' option is passed to the configure
options of Qt6 [1].

You can also build Intel64 binaries on arm64 Mac as follows.

 # Build Intel64 binaries
 python3 build_tools/build_qt.py --release --confirm_license  \
                                 --macos_cpus=x86_64

A known limitation is that building arm64 binaries on Intel64 mac does not
currently work though.

If '--macos_cpus' is not specified, Qt6 binaries will be built for the host CPU
architecture as it used to be.

 [1]: https://doc.qt.io/qt-6.5/macos-building.html#step-2-build-the-qt-library

PiperOrigin-RevId: 562439404

docs/build_mozc_in_osx.md

@@ -85,6 +85,18 @@ You can also specify `--debug` option to build debug version of Mozc.
 python3 build_tools/build_qt.py --release --debug --confirm_license
 ```
 
+You can also specify `--macos_cpus` option, which has the same semantics as the
+[same name option in Bazel](https://bazel.build/reference/command-line-reference#flag--macos_cpus),
+for cross-build including building a Universal macOS Binary.
+
+```
+# Building x86_64 binaries regardless of the host CPU architecture.
+python3 build_tools/build_qt.py --release --debug --confirm_license --macos_cpus=x86_64
+
+# Building Universal macOS Binary for both x86_64 and arm64.
+python3 build_tools/build_qt.py --release --debug --confirm_license --macos_cpus=x86_64,arm64
+```
+
 You can skip this process if you have already installed Qt prebuilt binaries.
 
 -----

src/build_tools/build_qt.py

@@ -253,6 +253,7 @@ def make_configure_options(args: argparse.Namespace) -> list[str]:
     A list of configure options to be passed to configure of Qt.
   Raises:
     ValueError: When Qt major version is not 6.
+    ValueError: When --macos_cpus=arm64 is set on Intel64 mac.
   """
 
   qt_version = get_qt_version(args)
@@ -283,6 +284,7 @@ def make_configure_options(args: argparse.Namespace) -> list[str]:
                           '-nomake', 'examples',
                           '-nomake', 'tests',
                          ]
+  cmake_options = []
 
   if is_mac():
     qt_configure_options += [
@@ -290,6 +292,20 @@ def make_configure_options(args: argparse.Namespace) -> list[str]:
         '-qt-libpng',
         '-qt-pcre',
     ]
+    if args.macos_cpus:
+      macos_cpus = args.macos_cpus.split(',')
+      host_arch = os.uname().machine
+      if host_arch == 'x86_64' and macos_cpus == ['arm64']:
+        # Haven't figured out how to make this work...
+        raise ValueError('--macos_cpus=arm64 on Intel64 mac is not supported.')
+      # 'x86_64' needs to be the first entry if exists.
+      # https://doc-snapshots.qt.io/qt6-6.5/macos-building.html#step-2-build-the-qt-library
+      if 'x86_64' in macos_cpus and macos_cpus[0] != 'x86_64':
+        macos_cpus.remove('x86_64')
+        macos_cpus = ['x86_64'] + macos_cpus
+      cmake_options += [
+          '-DCMAKE_OSX_ARCHITECTURES:STRING=' + ';'.join(macos_cpus),
+      ]
   elif is_windows():
     qt_configure_options += ['-c++std', 'c++20',
                              '-force-debug-info',
@@ -312,7 +328,8 @@ def make_configure_options(args: argparse.Namespace) -> list[str]:
   if qt_src_dir != qt_dest_dir:
     qt_configure_options += ['-prefix', str(qt_dest_dir)]
 
-  return qt_configure_options
+  return qt_configure_options + ((['--'] + cmake_options) if cmake_options
+                                 else [])
 
 
 def parse_args() -> argparse.Namespace:
@@ -339,6 +356,12 @@ def parse_args() -> argparse.Namespace:
   if is_windows():
     parser.add_argument('--vcvarsall_path', help='Path of vcvarsall.bat',
                         type=str, default=None)
+  elif is_mac():
+    parser.add_argument('--macos_cpus',
+                        help=('comma-separated CPU archs for mac Build (e.g. '
+                              '"arm64", "x86_64,arm64"). Corresponds to the '
+                              'same option in Bazel.'),
+                        type=str, default=None)
   return parser.parse_args()