[Ada] Do not use exponentiation for common bases in floating-point Value

[Ada] Do not use exponentiation for common bases in floating-point Value

gcc/ada/

	* Makefile.rtl (GNATRTL_NONTASKING_OBJS): Likewise.
	* exp_imgv.adb (Expand_Value_Attribute): Use RE_Value_Long_Float in
	lieu of RE_Value_Long_Long_Float as fallback for fixed-point types.
	Also use it for Long_Long_Float if it has same size as Long_Float.
	* libgnat/s-imgrea.adb: Replace Powten_Table with Powen_LLF.
	* libgnat/s-powflt.ads: New file.
	* libgnat/s-powlfl.ads: Likewise.
	* libgnat/s-powtab.ads: Rename to...
	* libgnat/s-powllf.ads: ...this.
	* libgnat/s-valflt.ads: Add with clause for System.Powten_Flt and
	pass its table as actual parameter to System.Val_Real.
	* libgnat/s-vallfl.ads: Likewise for System.Powten_LFlt.
	* libgnat/s-valllf.ads: Likewise for System.Powten_LLF.
	* libgnat/s-valrea.ads: Add Maxpow and Powten_Address parameters.
	* libgnat/s-valrea.adb: Add pragma Warnings (Off).
	(Need_Extra): New boolean constant.
	(Precision_Limit): Set it according to Need_Extra.
	(Impl): Adjust actual parameter.
	(Integer_to_Rea): Add assertion on the machine radix. Take into
	account the extra digit only if Need_Extra is true.  Reimplement
	the computation of the final value for bases 2, 4, 8, 10 and 16.
	* libgnat/s-valued.adb (Impl): Adjust actual parameter.
	(Scan_Decimal): Add pragma Unreferenced.
	(Value_Decimal): Likewise.
	* libgnat/s-valuef.adb (Impl): Adjust actual parameter.
	* libgnat/s-valuer.ads (Floating): Remove.
	(Round): New formal parameter.
	* libgnat/s-valuer.adb (Round_Extra): New procedure.
	(Scan_Decimal_Digits): Use it to round the extra digit if Round
	is set to True in the instantiation.
	(Scan_Integral_Digits): Likewise.