GCN, nvptx offloading: Restrain 'WARNING: program timed out.' while in 'dynamic_cast...

GCN, nvptx offloading: Restrain 'WARNING: program timed out.' while in 'dynamic_cast' only for effective-target 'offload_device' [PR119692]

In PR119692 "C++ 'typeinfo', 'vtable' vs. OpenACC, OpenMP 'target' offloading":

> --- Comment #8 from Rainer Orth <ro at gcc dot gnu.org> ---
> The last commit made things worse on sparc-sun-solaris2.11: since that one
> (dg-timeout 10) I regularly get
>
> WARNING: libgomp.c++/target-exceptions-bad_cast-1.C (test for excess errors)
> program timed out.
> FAIL: libgomp.c++/target-exceptions-bad_cast-1.C (test for excess errors)
> UNRESOLVED: libgomp.c++/target-exceptions-bad_cast-1.C compilation failed to produce executable
> UNRESOLVED: libgomp.c++/target-exceptions-bad_cast-1.C scan-tree-dump-times optimized "gimple_call <__cxa_bad_cast, " 1
>
> Before that, the test had no issue.  Compiling the test on an unloaded system
> usually takes less than 1 sec, but when fully loaded, times can go up.

To keep things simple, let's restrict this temporary (yeah...) workaround to
apply only for effective-target 'offload_device', just like the
'dg-xfail-run-if' itself.

	PR target/119692
	libgomp/
	* testsuite/libgomp.c++/pr119692-1-4.C: '{ dg-timeout 10 { target offload_device } }'.
	* testsuite/libgomp.c++/pr119692-1-5.C: Likewise.
	* testsuite/libgomp.c++/target-exceptions-bad_cast-1.C: Likewise.
	* testsuite/libgomp.c++/target-exceptions-bad_cast-2.C: Likewise.
	* testsuite/libgomp.oacc-c++/exceptions-bad_cast-1.C: Likewise.
	* testsuite/libgomp.oacc-c++/exceptions-bad_cast-2.C: Likewise.

(cherry picked from commit aa143261bdf6db4334b3fcad7768b53e231f998e)