Windows: Fix the build against complete LLVM packages

When compiling a dummy project for determining config values,
CMake is fooled to use clang++ as a compiler if it finds it.
Force it to use MSVC as is done for the build.

Change-Id: Ic1031a9aa078c0d05adf6495b4db665a0813e3f9
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
(cherry picked from commit bda973a2b0a288d0bc7390244ce6b563fe8dbe34)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 15 insertions, 5 deletions

diff --git a/build_scripts/main.py b/build_scripts/main.py
index a0b9335bb..82b0f31aa 100644
--- a/build_scripts/main.py
+++ b/build_scripts/main.py
@@ -76,7 +76,7 @@ from setuptools import Command
 from .qtinfo import QtInfo
 from .utils import (rmtree, detect_clang, copyfile, copydir, run_process_output, run_process,
                     update_env_path, init_msvc_env, filter_match, macos_fix_rpaths_for_library,
-                    linux_fix_rpaths_for_library)
+                    linux_fix_rpaths_for_library, platform_cmake_options)
 from .platforms.unix import prepare_packages_posix
 from .platforms.windows_desktop import prepare_packages_win32
 from .wheel_override import wheel_module_exists, get_bdist_wheel_override
@@ -652,6 +652,8 @@ class PysideBuild(_build, DistUtilsCommandMixin, BuildInfoCollectorMixin):
             cmake_cmd.append("-DCMAKE_INSTALL_RPATH_USE_LINK_PATH=yes")
             cmake_cmd.append("-DUSE_PYTHON_VERSION=3.6")
 
+        cmake_cmd += platform_cmake_options()
+
         if sys.platform == 'darwin':
             if OPTION["MACOS_ARCH"]:
                 # also tell cmake which architecture to use
@@ -688,10 +690,6 @@ class PysideBuild(_build, DistUtilsCommandMixin, BuildInfoCollectorMixin):
             deployment_target = macos_pyside_min_deployment_target()
             cmake_cmd.append(f"-DCMAKE_OSX_DEPLOYMENT_TARGET={deployment_target}")
             os.environ['MACOSX_DEPLOYMENT_TARGET'] = deployment_target
-        elif sys.platform == 'win32':
-            # Prevent cmake from auto-detecting clang if it is in path.
-            cmake_cmd.append("-DCMAKE_C_COMPILER=cl.exe")
-            cmake_cmd.append("-DCMAKE_CXX_COMPILER=cl.exe")
 
         if not OPTION["SKIP_DOCS"]:
             # Build the whole documentation (rst + API) by default
diff --git a/build_scripts/qtinfo.py b/build_scripts/qtinfo.py
index 749342679..f038adddc 100644
--- a/build_scripts/qtinfo.py
+++ b/build_scripts/qtinfo.py
@@ -44,6 +44,8 @@ import subprocess
 import tempfile
 from pathlib import Path
 
+from .utils import platform_cmake_options
+
 
 _CMAKE_LISTS = """cmake_minimum_required(VERSION 3.16)
 project(dummy LANGUAGES CXX)
@@ -264,6 +266,7 @@ class QtInfo(object):
                 cmd = [self._cmake_command, '-G', 'Ninja', '.']
                 qt_prefix = self.prefix_dir
                 cmd.extend([f'-DCMAKE_PREFIX_PATH={qt_prefix}'])
+                cmd += platform_cmake_options()
 
                 # FIXME Python 3.7: Use subprocess.run()
                 proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=False,
diff --git a/build_scripts/utils.py b/build_scripts/utils.py
index d5cfd8d67..45e7bdcd7 100644
--- a/build_scripts/utils.py
+++ b/build_scripts/utils.py
@@ -244,6 +244,15 @@ def init_msvc_env(platform_arch, build_type):
     log.info("Done initializing MSVC env")
 
 
+def platform_cmake_options():
+    result = []
+    if sys.platform == 'win32':
+        # Prevent cmake from auto-detecting clang if it is in path.
+        result.append("-DCMAKE_C_COMPILER=cl.exe")
+        result.append("-DCMAKE_CXX_COMPILER=cl.exe")
+    return result
+
+
 def copyfile(src, dst, force=True, vars=None, force_copy_symlink=False,
              make_writable_by_owner=False):
     if vars is not None: