Don't mark OpenACC auto loops as independent inside acc parallel regions

Don't mark OpenACC auto loops as independent inside acc parallel regions

2018-09-20  Cesar Philippidis  <cesar@codesourcery.com>

	gcc/
	* omp-low.c (lower_oacc_head_mark): Don't mark OpenACC auto
	loops as independent inside acc parallel regions.

	gcc/testsuite/
	* c-c++-common/goacc/loop-auto-1.c: Adjust test case to conform to
	the new behavior of the auto clause in OpenACC 2.5.
	* c-c++-common/goacc/loop-auto-2.c: Likewise.
	* gcc.dg/goacc/loop-processing-1.c: Likewise.
	* c-c++-common/goacc/loop-auto-3.c: New test.
	* gfortran.dg/goacc/loop-auto-1.f90: New test.

	libgomp/
	* testsuite/libgomp.oacc-c-c++-common/loop-auto-1.c: Adjust test case
	to conform to the new behavior of the auto clause in OpenACC 2.5.

(cherry picked from openacc-gcc-9-branch commit
6acf40a4364ccab3b71c3b58bf9ba5f16d19dc27)