[Ada] Usage of signed type in array bounds in CCG

[Ada] Usage of signed type in array bounds in CCG

2019-07-22  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* exp_ch4.adb (Size_In_Storage_Elements): Improve the expansion
	to handle array indexes that are modular type.
	(Expand_N_Allocator): For 32-bit targets improve the generation
	of the runtime check associated with large arrays supporting
	arrays initialized with a qualified expression.
	* libgnat/s-imenne.adb (Image_Enumeration_8,
	Image_Enumeration_16, Image_Enumeration_32): Define the index of
	Index_Table with range Natural'First .. Names'Length since in
	the worst case all the literals of the enumeration type would be
	single letter literals and the Table built by the frontend would
	have as many components as the length of the names string. As a
	result of this enhancement, the internal tables declared using
	Index_Table have a length closer to the real needs, thus
	avoiding the declaration of large arrays on 32-bit CCG targets.

From-SVN: r273685