cmake-gui: Always use "C" locale for numbers (#16099)

Set LC_NUMERIC = "C" at startup after Qt initializes the application
because Qt may have adopted the current locale from the environment.
CMake does not define behavior for non-C-locale numeric behavior.

Source/QtDialog/CMakeSetup.cxx

@@ -94,6 +94,8 @@ int main(int argc, char** argv)
 
   QApplication app(argc, argv);
 
+  setlocale(LC_NUMERIC, "C");
+
 #if defined(CMAKE_ENCODING_UTF8)
   QTextCodec* utf8_codec = QTextCodec::codecForName("UTF-8");
   QTextCodec::setCodecForLocale(utf8_codec);