Handle 'omp declare target' attribute set for both OpenACC and OpenMP 'target' [PR894...

Handle 'omp declare target' attribute set for both OpenACC and OpenMP 'target' [PR89433, PR93465]

... which as of PR89433 commit b48f44bf77a39fefc238a16cf1225c6464c82406 causes
an ICE.  Not sure if this is actually supposed to be valid or invalid code.
Until the interactions between OpenACC and OpenMP 'target' get defined
properly, make this a compile-time error.

	gcc/
	PR middle-end/89433
	PR middle-end/93465
	* omp-general.c (oacc_verify_routine_clauses): Diagnose if
	"#pragma omp declare target" has also been applied.
	gcc/testsuite/
	PR middle-end/89433
	PR middle-end/93465
	* c-c++-common/goacc-gomp/pr93465-1.c: New file.