Set charset for source and execution on Windows

- For the discussion after doxygen#10084
is merged.
- Keep minimal imports in QueryCodePage.py as reviewed

.editorconfig

@@ -3,6 +3,7 @@
 [*]
 indent_style = space
 indent_size = 2
+charset = utf-8
 
 [*.py]
 indent_size = 4

CMakeLists.txt

@@ -202,6 +202,7 @@ endif()
 
 include(cmake/CompilerWarnings.cmake)
 include(cmake/Coverage.cmake)
+include(cmake/WindowsEncoding.cmake)
 
 add_subdirectory(deps)
 add_subdirectory(libversion)

cmake/QueryCodePage.py

@@ -0,0 +1,21 @@
+import platform
+
+def is_windows():
+    return platform.system().lower() == "windows"
+
+if is_windows():
+    from winreg import OpenKey, QueryValueEx, HKEY_LOCAL_MACHINE, KEY_READ
+
+if __name__ == '__main__':
+    if is_windows():
+        root = HKEY_LOCAL_MACHINE
+        subkey = R'SYSTEM\CurrentControlSet\Control\Nls\CodePage'
+
+        key = OpenKey(root, subkey, 0, KEY_READ)
+        name = 'ACP'
+
+        try:
+            codepage, _ = QueryValueEx(key, name)
+            print(codepage)
+        except WindowsError:
+            print('Failed to get code page')

cmake/WindowsEncoding.cmake

@@ -0,0 +1,18 @@
+if(CMAKE_C_COMPILER_ID STREQUAL "MSVC" OR CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+  include(FindPythonInterp)
+  execute_process(
+    COMMAND ${PYTHON_EXECUTABLE} "${CMAKE_SOURCE_DIR}/cmake/QueryCodePage.py"
+    WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
+    RESULT_VARIABLE ReturnCode
+    OUTPUT_VARIABLE CodePage
+  )
+  message(STATUS "CodePage is ${CodePage}")
+  if("${CodePage}" STREQUAL "936")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /source-charset:utf-8 /execution-charset:gbk")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /source-charset:utf-8 /execution-charset:gbk")
+  else()
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /utf-8")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /utf-8")
+  endif()
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /bigobj") # /bigobj needed for language.cpp on 64bit
+endif()