Update GNU Fortran documentation (6.1.0, 5.4.0, 4.9.3)
Update GNU Fortran documentation (6.1.0, 5.4.0, 4.9.3)

rlugojr/devdocs,webcoding/devdocs,webcoding/devdocs,rlugojr/devdocs,yosiat/devdocs,rlugojr/devdocs,webcoding/devdocs,yosiat/devdocs,yosiat/devdocs