To build RPM use:

tar cvzf SDL_gfx-2.0.15.tar.gz SDL_gfx-2.0.15

cp SDL_gfx-2.0.15.tar.gz /usr/src/RPM/SOURCES/SDL_gfx-2.0.15.tar.gz
or
cp SDL_gfx-2.0.15.tar.gz /usr/src/redhat/SOURCES/SDL_gfx-2.0.15.tar.gz

rpm -ba SDL_gfx-2.0.15/SDL_gfx.spec
or
rpmbuild -ba SDL_gfx-2.0.15/SDL_gfx.spec