Incorrect compile_commands.json is generated by "NMake Makefiles" generator

Each command field in compile_commands.json contains pairs of @<<\n and \n<< inside a string literal:

  "command": "C:\\PROGRA~2\\MICROS~1.0\\VC\\bin\\cl.exe @<<
 /nologo (...)
<<",

It's not allowed as JSON string literals cannot contain control characters like \n (see specs at http://json.org)

This is of course due to

# for nmake make long command lines are redirected to a file
# with the following syntax, see Windows-bcc32.cmake for use
if(CMAKE_GENERATOR MATCHES "NMake")
  set(CMAKE_START_TEMP_FILE "@<<\n")
  set(CMAKE_END_TEMP_FILE "\n<<")
endif()

But I think it should be filtered out while generating compile_commands.json