Add support for printing value of DWARF-based fixed-point type objects

Add support for printing value of DWARF-based fixed-point type objects

This commit introduces a new kind of type, meant to describe
fixed-point types, using a new code added specifically for
this purpose (TYPE_CODE_FIXED_POINT).

It then adds handling of fixed-point base types in the DWARF reader.

And finally, as a first step, this commit adds support for printing
the value of fixed-point type objects.

Note that this commit has a known issue: Trying to print the value
of a fixed-point object with a format letter (e.g. "print /x NAME")
causes the wrong value to be printed because the scaling factor
is not applied. Since the fix for this issue is isolated, and
this is not a regression, the fix will be made in a pach of its own.
This is meant to simplify review and archeology.

Also, other functionalities related to fixed-point type handling
(ptype, arithmetics, etc), will be added piecemeal as well, for
the same reasons (faciliate reviews and archeology). Related to this,
the testcase gdb.ada/fixed_cmp.exp is adjusted to compile the test
program with -fgnat-encodings=all, so as to force the use of GNAT
encodings, rather than rely on the compiler's default to use them.
The intent is to enhance this testcase to also test the pure DWARF
approach using -fgnat-encodings=minimal as soon as the corresponding
suport gets added in. Thus, the modification to the testcase is made
in a way that it prepares this testcase to be tested in both modes.

gdb/ChangeLog:

        * ada-valprint.c (ada_value_print_1): Add fixed-point type handling.
        * dwarf2/read.c (get_dwarf2_rational_constant)
        (get_dwarf2_unsigned_rational_constant, finish_fixed_point_type)
        (has_zero_over_zero_small_attribute): New functions.
        read_base_type, set_die_type): Add fixed-point type handling.
        * gdb-gdb.py.in: Add fixed-point type handling.
        * gdbtypes.c: #include "gmp-utils.h".
        (create_range_type, set_type_code): Add fixed-point type handling.
        (init_fixed_point_type): New function.
        (is_integral_type, is_scalar_type): Add fixed-point type handling.
        (print_fixed_point_type_info): New function.
        (recursive_dump_type, copy_type_recursive): Add fixed-point type
        handling.
        (fixed_point_type_storage): New typedef.
        (fixed_point_objfile_key): New static global.
        (allocate_fixed_point_type_info, is_fixed_point_type): New functions.
        (fixed_point_type_base_type, fixed_point_scaling_factor): New
        functions.
        * gdbtypes.h: #include "gmp-utils.h".
        (enum type_code) <TYPE_SPECIFIC_FIXED_POINT>: New enum.
        (union type_specific) <fixed_point_info>: New field.
        (struct fixed_point_type_info): New struct.
        (INIT_FIXED_POINT_SPECIFIC, TYPE_FIXED_POINT_INFO): New macros.
        (init_fixed_point_type, is_fixed_point_type)
        (fixed_point_type_base_type, fixed_point_scaling_factor)
        (allocate_fixed_point_type_info): Add declarations.
        * valprint.c (generic_val_print_fixed_point): New function.
        (generic_value_print): Add fixed-point type handling.
        * value.c (value_as_address, unpack_long): Add fixed-point type
        handling.

gdb/testsuite/ChangeLog:

        * gdb.ada/fixed_cmp.exp: Force compilation to use -fgnat-encodings=all.
        * gdb.ada/fixed_points.exp: Add fixed-point variables printing tests.
        * gdb.ada/fixed_points/pck.ads, gdb.ada/fixed_points/pck.adb:
        New files.
        * gdb.ada/fixed_points/fixed_points.adb: Add use of package Pck.

        * gdb.dwarf2/dw2-fixed-point.c, gdb.dwarf2/dw2-fixed-point.exp:
        New files.