Enabling OpenACC

To activate the OpenACC extensions for C/C++ and Fortran, the compile-time flag -fopenacc must be specified. This enables the OpenACC directive #pragma acc in C/C++ and !$acc directives in free form, c$acc, *$acc and !$acc directives in fixed form, !$ conditional compilation sentinels in free form and c$, *$ and !$ sentinels in fixed form, for Fortran. The flag also arranges for automatic linking of the OpenACC runtime library (OpenACC Runtime Library Routines).

See https://gcc.gnu.org/wiki/OpenACC for more information.

A complete description of all OpenACC directives accepted may be found in the OpenACC Application Programming Interface manual, version 2.6.