[Ada] Fix uniqueness of address for aliased objects

[Eric Botcazou]

Two aliased objects must have distinct addresses, even if they have size zero, 
so we make sure to allocate at least one byte for them.

Tested on x86-64/Linux, applied on the mainline.


2020-05-08  Eric Botcazou  <ebotcazou@adacore.com>

	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Variable>: Force at
	least the unit size for an aliased object of a constrained nominal
	subtype whose size is variable.


2020-05-08  Eric Botcazou  <ebotcazou@adacore.com>

	* gnat.dg/addr15.adb: New test.

-- 
Eric Botcazou
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