c++,coroutines: Stabilize names of promoted slot vars [PR101118].

c++,coroutines: Stabilize names of promoted slot vars [PR101118].

When we need to 'promote' a value (i.e. store it in the coroutine frame) it
is given a frame entry name.  This was based on the DECL_UID for slot vars.
However, when LTO is used, the names from multiple TUs become visible at the
same time, and the DECL_UIDs usually differ between units.  This leads to a
"ODR mismatch" warning for the frame type.

The fix here is to use the current promoted temporaries count to produce
the name, this is stable between TUs and computed per coroutine.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
	PR c++/101118

gcc/cp/ChangeLog:

	* coroutines.cc (flatten_await_stmt): Use the current count of
	promoted temporaries to build a unique name for the frame entries.

(cherry picked from commit fc4cde2e6aa4d6ebdf7f70b7b4359fb59a1915ae)