[c++] Don't emit exception tables for UI_NONE

[c++] Don't emit exception tables for UI_NONE

If a target does not support exceptions, it can indicate this by returning
UI_NONE in TARGET_EXCEPT_UNWIND_INFO.  Currently the compiler still emits
exception tables for such a target.

This patch makes sure that no exception tables are emitted if the target does
not support exceptions.  This allows us to remove a workaround in
TARGET_ASM_BYTE_OP in the nvptx port.

Build on x86_64 with nvptx accelerator, and tested libgomp.

Build and reg-tested on x86_64.

2018-08-03  Tom de Vries  <tdevries@suse.de>

	* common/config/nvptx/nvptx-common.c (nvptx_except_unwind_info): Return
	UI_NONE.
	* config/nvptx/nvptx.c (TARGET_ASM_BYTE_OP): Remove define.
	* except.c (output_function_exception_table): Do early exit if
	targetm_common.except_unwind_info (&global_options) == UI_NONE.

From-SVN: r263287