floating point operating in vhdl (fixed_pkg)

I did as Tricky suggested and both my Quartus and ModelSim projects compile! I had to rename "ieee_proposed" to "ieee" as suggested by flz47655.

Just so I understand why this works, correct me if I'm wrong:

- Quartus compiles the 1993 (compatible) fixed_pkg into its ieee library

- ModelSim also compiles the 1993 (compatible) fixed_pkg into its ieee library, ignoring its 2008 version since I used the _c.vhdl files for the fixed_pkg

- this would not have worked if the source files "fixed_float_types" and "fixed_pkg" were named the same in both projects since ModelSim has its own version of the files