qbs: fix installing doc dependenices on macOS and Windows

python still aliases to python 2.7 on macOS, so we need a smarter way to
find python3.

Change-Id: I229d8c1e124fb599119991b44c0f6d88d39b1684
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

.github/workflows/build_cmake.yml

@@ -330,8 +330,12 @@ jobs:
             message(FATAL_ERROR "Failed to install dependencies")
           endif()
         endif()
+        find_package(Python3 REQUIRED COMPONENTS Interpreter)
+        # hack to replace 32-bit python found by this script with 64-bit one
+        # required for linking qtcreatorcdbext
+        string(REPLACE "x86" "x64" Python3_EXECUTABLE "${Python3_EXECUTABLE}")
         execute_process(
-          COMMAND python -m pip install --user beautifulsoup4 lxml
+          COMMAND ${Python3_EXECUTABLE} -m pip install --user beautifulsoup4 lxml
           RESULT_VARIABLE result
         )
         if (NOT result EQUAL 0)
@@ -394,6 +398,9 @@ jobs:
           set(ELFUTILS_OPTION)
         endif()
 
+        find_package(Python3 REQUIRED COMPONENTS Interpreter)
+        string(REPLACE "x86" "x64" Python3_EXECUTABLE "${Python3_EXECUTABLE}")
+
         execute_process(
           COMMAND python
             -u
@@ -403,6 +410,7 @@ jobs:
             --build build
             --qt-path "${{ steps.qt.outputs.qt_dir }}"
             --llvm-path "${{ steps.libclang.outputs.libclang_dir }}"
+            --python3 "${Python3_EXECUTABLE}"
             --with-tests
             ${CDB_OPTION}
             ${ELFUTILS_OPTION}

scripts/build.py

@@ -132,6 +132,7 @@ def build_qtcreator(args, paths):
 
     if args.python3:
         cmake_args += ['-DPYTHON_EXECUTABLE=' + args.python3]
+        cmake_args += ['-DPython3_EXECUTABLE=' + args.python3]
 
     if args.module_paths:
         module_paths = [common.to_posix_path(os.path.abspath(fp)) for fp in args.module_paths]