[og9] Add support for constructors and destructors on GCN

[og9] Add support for constructors and destructors on GCN

2019-05-22  Kwok Cheung Yeung  <kcy@codesourcery.com>
	    Andrew Stubbs  <amd@codesourcery.com>

	Backport from mainline:

	* config.gcc (gcc_cv_initfini_array): Set for AMD GCN.
	* config/gcn/gcn-run.c (init_array_kernel, fini_array_kernel): New.
	(kernel): Rename to...
	(main_kernel): ... this.
	(load_image): Load _init_array and _fini_array kernels.
	(run): Add argument for kernel to run.
	(main): Run init_array_kernel before main_kernel, and
	fini_array_kernel after.
	* config/gcn/gcn.c (gcn_handle_amdgpu_hsa_kernel_attribute): Allow
	amdgpu_hsa_kernel attribute on functions.
	(gcn_disable_constructors): Delete.
	(TARGET_ASM_CONSTRUCTOR, TARGET_ASM_DESTRUCTOR): Delete.
	* config/gcn/crt0.c (size_t): Define.
	(_init_array, _fini_array): New.
	(__preinit_array_start, __preinit_array_end,
	__init_array_start, __init_array_end,
	__fini_array_start, __fini_array_end): Declare weak references.

(cherry picked from openacc-gcc-9-branch commit
9f1f40c95faab3d935f75280d5063a0344f020cf)