Extend test suite coverage for OpenACC 'self' clause for compute constructs

Extend test suite coverage for OpenACC 'self' clause for compute constructs

... on top of what was provided in recent
commit 3a3596389c2e539cb8fd5dc5784a4e2afe193a2a
"OpenACC 2.7: Implement self clause for compute constructs".

	gcc/testsuite/
	* c-c++-common/goacc/if-clause-2.c: Enhance.
	* c-c++-common/goacc/self-clause-1.c: Likewise.
	* c-c++-common/goacc/self-clause-2.c: Likewise.
	* gfortran.dg/goacc/if.f95: Likewise.
	* gfortran.dg/goacc/kernels-tree.f95: Likewise.
	* gfortran.dg/goacc/parallel-tree.f95: Likewise.
	* gfortran.dg/goacc/self.f95: Likewise.
	libgomp/
	* testsuite/libgomp.oacc-c-c++-common/if-1.c: Enhance.
	* testsuite/libgomp.oacc-c-c++-common/self-1.c: Likewise.
	* testsuite/libgomp.oacc-fortran/if-1.f90: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/if-self-1.c: New.
	* testsuite/libgomp.oacc-fortran/self-1.f90: Likewise.