Added lib path for macOS to find openblas

[vietlq]

Added lib path for macOS to find openblas.

This shouldn't affect other OS that already find openblas. macOS doesn't have libopenblas.[a|dylib] in /usr/local/lib or /usr/lib.

[vietlq]

Found another missing library -lgfortran for Ubuntu Trusty:

# (cd _build/default && /home/travis/.opam/4.04.2/bin/ocamlmklib.opt -g -o src/owl/owl_stubs src/owl/owl_dense_common_c.o src/owl/owl_dense_common_vec_cmp.o src/owl/owl_dense_common_vec_map.o src/owl/owl_dense_common_vec_fold.o src/owl/owl_cblas_generated_stub.o src/owl/owl_lapacke_generated_stub.o -L/usr/local/lib/gcc/7 -L/usr/local/opt/openblas/lib -lopenblas -lgfortran -lm)

# /usr/bin/ld: cannot find -lgfortran

# collect2: error: ld returned 1 exit status

[tachukao]

@vietlq jbuilder finishes building owl without any errors after I added in -L/usr/local/opt/openblas/lib. However, when I try to use it in utop, it complains

Cannot load required shared library dllowl_stubs.
Reason: dllowl_stubs.so: dlopen(dllowl_stubs.so, 138): image not found.

any ideas? thanks!

UPDATE:
works in utop now that I moved dllowl_stubs.so from ~/.opam/.../lib/stubslibs/ to ~/.opam/.../lib/stublibs/

[ryanrhymes]

@vietlq Thanks again for fixing this 💯

@tachukao yes, the extra s in stubslibs relates to an issue in opam which has been fixed since opam 2.0 beta 4.