Can't build with PGI because of `restrict` keyword

[chuckatkins]

Currently unable to build with PGI because of API functions named restrict which is a reserved C keyword. Renaming the API functions to something else not conflicting with a reserved keyword allows the build to be successful with PGI.

[chuckatkins]

Note that since this is part of MGARD's public API, it also prevents a downstream consumer to build with MGARD support and PGI.

[tugluk]

Solved with recent commit