ada: Fix unnesting generated loops with nested finalization procedure

The compiler can generate loops for creating array aggregates, for
example used during the initialization of variable. If the component
type of the array element requires finalization, the compiler also
creates a block and a nested procedure that need to be correctly
unnested if unnesting is enabled. During the unnesting transformation,
the scopes for these inner blocks need to be fixed and set to the
enclosing loop entity.

gcc/ada/

	* exp_ch7.adb (Contains_Subprogram): Recursively search for subp
	in loop's statements.
	(Unnest_Loop)<Fixup_Inner_Scopes>: New.
	(Unnest_Loop): Rename local variable for more clarity.
	* exp_unst.ads: Refresh comment.

• [DBH] gcc/ada/exp_ch7.adb
• [DBH] gcc/ada/exp_unst.ads

ada: Refine upper array bound for bit packed array

When using bit-packed arrays, the compiler creates new array subtypes of
1-bit component indexed by integers. The existing routine checks the
index subtype to find the min/max values. Bit-packed arrays being
indexed by integers, the routines gives up as returning the maximum
possible integer carries no useful information.

This change adds a simple max_value routine that can evaluate very
simple expressions by substituting variables by their min/max value.
Bit-packed array subtypes are currently declared as:

  subtype bp_array is packed_bytes1 (0 .. integer((1 * Var +  7) / 8 - 1));

The simple max_value evaluator handles the bare minimum for this
expression pattern.

gcc/ada/ChangeLog:

	* gcc-interface/utils.cc (max_value): New.
	* gcc-interface/gigi.h (max_value): New.
	* gcc-interface/decl.cc (gnat_to_gnu_entity) <E_Array_Subtype>:
	When computing gnu_min/gnu_max, try to use max_value if there is
	an initial expression.

• [DBH] gcc/ada/gcc-interface/decl.cc
• [DBH] gcc/ada/gcc-interface/gigi.h
• [DBH] gcc/ada/gcc-interface/utils.cc