[SOLLVE V&V] Add support for Fortran tests (#119)

* [SOLLVE V&V] Add support for Fortran tests

Need to add the CMAKE Flag TEST_SUITE_FORTRAN=ON

Plus, changed TEST_SUITE_OFFLOADING_FLAGS to
TEST_SUITE_OFFLOADING_<lang>_FLAGS where <lang>
is C, CXX, or Fortran

* [SOLLVE V&V] Add support for Fortran tests in the README

* [SOLLVE V&V] Add LD Lang Flags

Author: ajarmusch