[Ada] Better error message for aliased formal and atomic actual

[Pierre-Marie de Rodat]

The C.6 (12/3) clause makes it illegal to pass an atomic actual
parameter in a call corresponding to an aliased formal with a nonatomic
type.

This illegal case had been accepted up recently and started only to be
rejected as a by-product of the implementation of the C.6 (19) clause,
but the error message is confusing.

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

2019-12-13  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* sem_res.adb (Resolve_Actuals): Give canonical error for
	illegal case of atomic/volatile parameter also if the formal is
	aliased.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: patch.diff
Type: text/x-diff
Size: 399 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20191213/90a54573/attachment.bin>