Octave compatibility for ft_compile_mex

[apjanke]

This PR modifies ft_compile_mex for Octave compatibility.

Addresses #1027 (comment).

The big issue with Octave compatibility is that it picks up files inside @class directories when you cd in to them and sees them as global functions. This PR restructures ft_compile_mex to not change into the individual source directories when it's doing compiling. Also addresses differences in Octave mex()'s signature from Matlab's mex().

With this change, everything is compiling on Octave 4.4.1 on macOS for me, except mxSerialize and mxDeserialize.

Compiling MEX file src/mxSerialize_cpp ...
  mex -v /Users/janke/local/repos/fieldtrip/src/mxSerialize_cpp.cpp -I/Users/janke/local/repos/fieldtrip/src --output /Users/janke/local/repos/fieldtrip/src/mxSerialize_cpp
Undefined symbols for architecture x86_64:
  "mxSerialize(void const*)", referenced from:
      _mexFunction in mxSerialize_cpp.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
warning: mkoctfile: building exited with failure status
clang++ -std=gnu++11 -c  -fPIC -I/usr/local/Cellar/octave/4.4.1_6/include/octave-4.4.1/octave/.. -I/usr/local/Cellar/octave/4.4.1_6/include/octave-4.4.1/octave -I/usr/local/Cellar/octave/4.4.1_6/include  -D_THREAD_SAFE -pthread -I/Library/Java/JavaVirtualMachines/openjdk-11.0.2.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/openjdk-11.0.2.jdk/Contents/Home/include/darwin   -I. -I/Users/janke/local/repos/fieldtrip/src  /Users/janke/local/repos/fieldtrip/src/mxSerialize_cpp.cpp -o mxSerialize_cpp.o
clang++ -std=gnu++11 -I/usr/local/Cellar/octave/4.4.1_6/include/octave-4.4.1/octave/.. -I/usr/local/Cellar/octave/4.4.1_6/include/octave-4.4.1/octave -I/usr/local/Cellar/octave/4.4.1_6/include  -D_THREAD_SAFE -pthread -I/Library/Java/JavaVirtualMachines/openjdk-11.0.2.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/openjdk-11.0.2.jdk/Contents/Home/include/darwin -bundle -bundle_loader /usr/local/Cellar/octave/4.4.1_6/bin/octave-4.4.1  -o /Users/janke/local/repos/fieldtrip/src/mxSerialize_cpp.mex  mxSerialize_cpp.o   -L/usr/local/Cellar/octave/4.4.1_6/lib/octave/4.4.1 -L/usr/local/Cellar/octave/4.4.1_6/lib -loctinterp -loctave
mex compilation failed: -v /Users/janke/local/repos/fieldtrip/src/mxSerialize_cpp.cpp -I/Users/janke/local/repos/fieldtrip/src --output /Users/janke/local/repos/fieldtrip/src/mxSerialize_cpp
error: called from
    ft_compile_mex>my_mex at line 242 column 5
    ft_compile_mex>compile_mex_list at line 234 column 3
    ft_compile_mex at line 121 column 3
octave:11> ver
----------------------------------------------------------------------
GNU Octave Version: 4.4.1 (hg id: 1f46d371968c)
GNU Octave License: GNU General Public License
Operating System: Darwin 18.2.0 Darwin Kernel Version 18.2.0: Thu Dec 20 20:46:53 PST 2018; root:xnu-4903.241.1~1/RELEASE_X86_64 x86_64
----------------------------------------------------------------------

Looks like a problem with the MX API thing they're setting up in the defines.

// MX_API_VER has unfortunately not changed between R2013b and R2014a,
// so we use the new MATRIX_DLL_EXPORT_SYM as an ugly hack instead
#if defined(__cplusplus) && defined(MATRIX_DLL_EXPORT_SYM)
    #define EXTERN_C extern
    namespace matrix{ namespace detail{ namespace noninlined{ namespace mx_array_api{
#endif

It's not working on macOS for me under R2017b or R2018b because mex doesn't like the 'CFLAGS=''-std=c99 -fPIC''' argument.

Compiling MEX file external/fileexchange/CalcMD5 ...
Building with 'Xcode with Clang'.
Error using mex
error: invalid value 'c99 -fPIC' in '-std=c99 -fPIC'
note: use 'c89', 'c90', or 'iso9899:1990' for 'ISO C 1990' standard
note: use 'iso9899:199409' for 'ISO C 1990 with amendment 1' standard
note: use 'gnu89' or 'gnu90' for 'ISO C 1990 with GNU extensions' standard
note: use 'c99' or 'iso9899:1999' for 'ISO C 1999' standard
note: use 'gnu99' for 'ISO C 1999 with GNU extensions' standard
note: use 'c11' or 'iso9899:2011' for 'ISO C 2011' standard
note: use 'gnu11' for 'ISO C 2011 with GNU extensions' standard
note: use 'c17' or 'iso9899:2017' for 'ISO C 2017' standard
note: use 'gnu17' for 'ISO C 2017 with GNU extensions' standard

Error in ft_compile_mex>my_mex (line 244)
  mex(varargin{:});
Error in ft_compile_mex>compile_mex_list (line 233)
  my_mex(mex_args{:});
Error in ft_compile_mex (line 121)
  compile_mex_list(L, ftpath, force); 

References

• https://undocumentedmatlab.com/blog/serializing-deserializing-matlab-data