Add ptype support for DWARF-based fixed-point types

Note that the ptype information printed for types described
via pure DWARF debug info is slightly less informative as
the one printed when the information is encoded in the type's
name, via the GNAT encoding. As a result, the output in
the case of DWARF-described fixed point types is slightly
different. In pratice, this is no real loss because the information
not available in DWARF has no bearing on how the type is actually
stored in memory.

gdb/ChangeLog:

        * ada-typeprint.c (ada_print_type): Add handing of fixed-point
        range types.
        * c-typeprint.c (c_type_print_varspec_prefix)
        (c_type_print_varspec_suffix, c_type_print_base_1): Add
        TYPE_CODE_FIXED_POINT handling.
        * p-typeprint.c (pascal_type_print_varspec_prefix)
        (pascal_type_print_varspec_suffix): Likewise.
        * typeprint.c (print_type_fixed_point): New function.
        * typeprint.h (print_type_fixed_point): Add declaration.

gdb/testsuite/ChangeLog:

        * gdb.ada/fixed_points.exp: Add ptype tests.
        * gdb.dwarf2/dw2-fixed-point.exp: Likewise.