testsuite: don't declare printf in coro.h

testsuite: don't declare printf in coro.h

mingw stdio.h plays horrible games with extern "C++", but it also seems
sloppy for coro.h to declare printf in testcases that will also include
standard headers.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/coro.h: #include <stdio.h> instead of
	declaring puts/printf.
	* g++.dg/coroutines/torture/mid-suspend-destruction-0.C:
	#include <stdio.h>.
	* g++.dg/coroutines/pr95599.C: Use PRINT instead of puts.
	* g++.dg/coroutines/torture/call-00-co-aw-arg.C:
	* g++.dg/coroutines/torture/call-01-multiple-co-aw.C:
	* g++.dg/coroutines/torture/call-02-temp-co-aw.C:
	* g++.dg/coroutines/torture/call-03-temp-ref-co-aw.C:
	* g++.dg/coroutines/torture/co-await-00-trivial.C:
	* g++.dg/coroutines/torture/co-await-01-with-value.C:
	* g++.dg/coroutines/torture/co-await-02-xform.C:
	* g++.dg/coroutines/torture/co-await-03-rhs-op.C:
	* g++.dg/coroutines/torture/co-await-04-control-flow.C:
	* g++.dg/coroutines/torture/co-await-05-loop.C:
	* g++.dg/coroutines/torture/co-await-06-ovl.C:
	* g++.dg/coroutines/torture/co-await-07-tmpl.C:
	* g++.dg/coroutines/torture/co-await-08-cascade.C:
	* g++.dg/coroutines/torture/co-await-09-pair.C:
	* g++.dg/coroutines/torture/co-await-11-forwarding.C:
	* g++.dg/coroutines/torture/co-await-12-operator-2.C:
	* g++.dg/coroutines/torture/co-await-13-return-ref.C:
	* g++.dg/coroutines/torture/co-await-14-return-ref-to-auto.C:
	* g++.dg/coroutines/torture/pr95003.C: Likewise.