[Ada] Generate Machine, Model and Rounding FP attributes in line

[Arnaud Charlet <charlet at adacore dot com>]

This change makes it so that the Machine, Model and Rounding FP attributes
are generated in line by the compiler (in conjunction with a conversion to
an integer type for the third) and optimized on architectures that do not
make use of internal extended precision in the FPU.

The following function must be optimized into a return on PowerPC and SPARC:

function Machine (F: Float) return Float is
begin
  return Float'Machine (F);
end;

Tested on x86_64-pc-linux-gnu, committed on trunk

2014-08-01  Eric Botcazou  <ebotcazou@adacore.com>

	* exp_attr.adb (Expand_N_Attribute_Reference): Check whether
	expansion can be avoid for Machine, Model and Rounding.
	(Is_Inline_Floating_Point_Attribute): Return true for Machine
	& Model, as well as Rounding if wrapped in a conversion to an
	integer type.
	* sem_res.adb (Simplify_Type_Conversion): Deal with Rounding as well.
	* gcc-interface/gigi.h (fp_arith_may_widen): Declare.
	* gcc-interface/utils.c (fp_arith_may_widen): New global variable.
	* gcc-interface/misc.c (enumerate_modes): Compute it.
	* gcc-interface/trans.c (FP_ARITH_MAY_WIDEN): Delete.
	(lvalue_required_for_attribute_p): Deal with Descriptor_Size,
	Machine and Model.
	(Attribute_to_gnu) <Attr_Model>: New case.
	<Attr_Machine>): Likewise.
	(convert_with_check): Test
	fp_arith_may_widen variable.

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