Define a "Fortran_FORMAT" target and source file property. Initialize
the target property from a "CMAKE_Fortran_FORMAT" variable. Interpret
values "FIXED" and "FREE" to indicate the source file format. Append
corresponding flags to the compiler command line.
This commit teaches CMake about the g95 compiler from
http://www.g95.org
We use 'G95' as the compiler id string, and add some basic flags.
See issue #9241.