Improve filenames for test cases of OpenACC combined directives

Improve filenames for test cases of OpenACC combined directives

	libgomp/
	* testsuite/libgomp.oacc-c-c++-common/combdir-1.c: Rename to...
	* testsuite/libgomp.oacc-c-c++-common/combined-directives-1.c:
	... this.  Add a description of the test at the top of the file.
	* testsuite/libgomp.oacc-fortran/combdir-1.f90: Rename file to...
	* testsuite/libgomp.oacc-fortran/combined-directives-1.f90:
	... this.  Add a description of the test at the top of the file.

Co-Authored-By: Cesar Philippidis <cesar@codesourcery.com>
From-SVN: r229518