[Ada] Fix internal error on bit-aligned component of function call

[Pierre-Marie de Rodat]

This fixes an internal error in the code generator triggered by a
reference generated by the front-end to a bit-aligned component of
the result of a function call.  Such a reference cannot be handled
by the code generator because the object is not aligned on a byte
boundary, so it is replaced by a renaming that is fully handled by
the front-end because of the potential nonstandard representation.

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

gcc/ada/

	* exp_util.adb (Remove_Side_Effects): Always generate a renaming
	that is handled by the front-end in the case of an indexed or a
	selected component whose prefix has a nonstandard representation.
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