[Ada] spurious misalignment warnings on misc UNC operations

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk

While processing an unchecked conversion of an address expression to an
access type, the compiler warns if the address is not known to be at least
as aligned as the access type expects.

gigi's 'known_alignment' function is what determines how aligned an address
expression is known to be. It turned out to miss code for a number of
legitimate address subexpression kinds, resulting in spurious warnings in
some circumstances.

The fix applied here adds the missing code for three such subexpressions.

The need for BIT_AND_EXPR and COND_EXPR is exposed by gnat.dg/alignment3.adb

2007-04-06  Olivier Hainque  <hainque@adacore.com>

	* utils2.c (known_alignment): Handle COMPOUND_EXPR, COND_EXPR and
	BIT_AND_EXPR. Handle also VIEW_CONVERT_EXPR, as the other conversion
	opcodes.

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