[OpenACC] bump version for 2.6 plus libgomp.texi update

[OpenACC] bump version for 2.6 plus libgomp.texi update

2020-02-03  Julian Brown  <julian@codesourcery.com>
            Tobias Burnus  <tobias@codesourcery.com>

	gcc/c-family/
	* c-cppbuiltin.c (c_cpp_builtins): Update _OPENACC define to 201711.

	gcc/
	* doc/invoke.texi: Update mention of OpenACC version to 2.6.

	gcc/fortran/
	* cpp.c (cpp_define_builtins): Update _OPENACC define to 201711.
	* intrinsic.texi: Update mentions of OpenACC version to 2.6.
	* gfortran.texi: Likewise. Remove experimental disclamer for OpenACC.
	* invoke.texi: Remove experimental disclamer for OpenACC.

	gcc/testsuite/
	* c-c++-common/cpp/openacc-define-3.c: Update expected value for
	_OPENACC define.
	* gfortran.dg/openacc-define-3.f90: Likewise.

	libgomp/
	* libgomp.texi (OpenACC Runtime Library Routines): Document *_async
	and *_finalize variants; document acc_attach and acc_detach; update
	references from OpenACC 2.0 to 2.6.
	* openacc.f90 (openacc_version): Update to 201711.
	* openacc_lib.h (openacc_version): Update to 201711.
	* testsuite/libgomp.oacc-fortran/openacc_version-1.f: Update expected
	openacc_version to 201711.
	* testsuite/libgomp.oacc-fortran/openacc_version-2.f90: Likewise.