Target FP: Perform Ada fixed-point scaling in target format

Target FP: Perform Ada fixed-point scaling in target format

One of the few still remaining uses of DOUBLEST in GDB is the Ada front-end
code that handles scaling of Ada fixed-point types.  The target format for
those types is some integer format; to convert those values to standard
floating-point representation, that integer needs to be multiplied by a
rational scale factor, given as a pair of numerator and denominator.

To avoid having to deal with long integer arithmetic, the current Ada
front-end code currently performs those scaling operations in host
DOUBLEST arithmetic.  To eliminate this use of DOUBLEST, this patch
changes the front-end to instead perform those operations in the
*target* floating-point format (chosing to use the target "long double").

The implementation is mostly straight-forward, using value_cast and
value_binop to perform the target operations.

Scanning in the scale numerator and denominator is now done into
a host "long long" instead of a DOUBLEST, which should be large
enough to hold all possible values.  (Otherwise, this can be replaced
by target-format target_float_from_string operations as well.)

Printing fixed-point types and values should be completely unchanges,
using target_float_to_string with the same format strings as current code.

gdb/ChangeLog:
2017-11-06  Ulrich Weigand  <uweigand@de.ibm.com>

	* ada-lang.c (cast_to_fixed): Reimplement in target arithmetic.
	(cast_from_fixed): Likewise.
	(ada_scaling_type): New function.
	(ada_delta): Return value instead of DOUBLEST.  Perform target
	arithmetic instead of host arithmetic.
	(scaling_factor): Rename to ...
	(ada_scaling_factor) ... this.  Make non-static.  Return value instead
	of DOUBLEST.  Perform target arithmetic instead of host arithmetic.
	(ada_fixed_to_float): Remove.
	(ada_float_to_fixed): Remove.
	* ada-lang.h (ada_fixed_to_float): Remove.
	(ada_float_to_fixed): Remove.
	(ada_delta): Return value instead of DOUBLEST.
	(ada_scaling_factor): Add prototype.

	* ada-typeprint.c: Include "target-float.h".
	(print_fixed_point_type): Perform target arithmetic instead of
	host arithmetic.
	* ada-valprint.c: Include "target-float.h".
	(ada_val_print_num): Perform target arithmetic instead of
	host arithmetic for fixed-point types.