Precompile headers: build failure when compiling Objective-C++ source files
If one uses the Ninja or Makefile generator, precompile headers support, and Objective-C++ files, the build will fail.
The Objective-C++ files (*.mm) need to be in the client CMake code marked with
This is due to the fact that CMake's precompile headers feature supports only the
C++ languages. Objective-C++ files appear in CMake as
C++ files, and there is no way they can be excluded / use an Objective-C++ tailored PCH file.
CMake needs to learn how to distinguish the Objective-C++ differently as C++. Using a
cmSystemTools::StringEndsWith(file, ".mm") seems very hackish.