Building gmtmex on Linux

While searching for documentation regarding building gmtmex on Linux, I noticed that the readme was looking for volunteers. With the steps outlined below, I am able to get GMT to work with my MATLAB project on Ubuntu 18.04. I am sure there is a more elegant way of achieving this, however, I thought it best to share this solution, since it does appear to work well.

With both MATLAB R2019a and GMT Version 6.1.0_3ede8d1_2019.08.04 installed in /home, in the gmtmex directory cloned from GitHub:

1. Built gmtmex object file as
`gcc -I$GMT_dir/include/gmt -I$MATLAB_dir/extern/include -O2 -Wall -m64 -fPIC -fno-strict-aliasing -std=c99 -DGMT_MATLAB -I$GMT_dir/include/gmt -c gmtmex.c`

2. Built gmtmex_parser object file as
`gcc -I$GMT_dir/include/gmt -I$MATLAB_dir/extern/include -O2 -Wall -m64 -fPIC -fno-strict-aliasing -std=c99 -DGMT_MATLAB -I$GMT_dir/include/gmt -c gmtmex_parser.c`

3. Compiled mex file as
`$MATLAB_dir/bin/mex -DGMT_MATLAB -I$GMT_dir/include/gmt -I/$GMT_dir/include/gmt/lib -I$MATLAB_dir/extern/include gmtmex.o gmtmex_parser.o -L$GMT_dir/lib -lgmt -L$MATLAB_dir/bin/glnxa64 -lmx -lmex -output gmtmex.mexa64`

Copied over the gmt.m and generated gmtmex.mexa64 files to $GMT_dir/bin, added $GMT_dir along with subfolders to MATLAB path.

In order to prevent runtime errors associated with MATLAB not being able to find shared libraries, launch MATLAB as:
`export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$GMT_dir/lib`
`export LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libtiff.so.5:/usr/lib/x86_64-linux-gnu/libstdc++.so.6`
`$MATLAB_dir/bin/matlab`

I hope this proves to be helpful. Please let me know in case further tests are required.