math/coinmp: Add an option for Fortran.

It can be convenient for performance to enable blas/lapack, which
necessarilly involves using the fortran interface. Leave it OFF by
default since it can interfere with some important consumers like
Apache OpenOffice.

Use the standard TEST_TARGET while here.

No need to bump the portversion as this doesn't affect the package.

PR: 219261
Approved by: cpm