coroutines: Await expressions are not allowed in handlers [PR 99710].

coroutines: Await expressions are not allowed in handlers [PR 99710].

C++20 [expr.await] / 2
An await-expression shall appear only in a potentially-evaluated expression
within the compound-statement of a function-body outside of a handler.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
	PR c++/99710

gcc/cp/ChangeLog:

	* coroutines.cc (await_statement_walker): Report an error if
	an await expression is found in a handler body.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/pr99710.C: New test.

(cherry picked from commit 650beb110538097b9c3e8600149b333a83e7e836)