Error handling response files

[mizvekov]

The mrdocs tool has trouble processing response files. This can be observed when processing the compile_commands.json output from a cmake project which relies on them, such as a project containing C++ 20 modules.

error: no such file or directory: '@tools/CMakeFiles/cpe2x.dir/cpe2x.cc.obj.modmap'

The error seems to indicate we are interpreting the response file command line option as a file path, including the leading '@'.

Response files are simple text files composed of multiple lines, each containing a single compiler command line argument.
Their purpose is to avoid hitting implementation limits related to long command lines.

As an example, here are the contents from the above response file:

-fmodule-file=psx.base=psx/CMakeFiles/psx.base.obj.dir/psx.base.pcm
-fmodule-file=std=ext/cxx/CMakeFiles/ext.cxx.obj.dir/std.pcm