NAG: Fix using Fortran modules from their output directory
The NAG Fortran compiler's
-mdir flag sets the module output
directory but does not add the directory to the search path for using
modules. This is inconsistent with other compilers like the GNU Fortran
-J flag that does both. In order to make these consistent,
add the module output directory with a
-I flag on the NAG Fortran
compiler so that it will be searched when using modules too.
We already do this for the XL Fortran compiler since !4405 (merged).