[nvptx] Ignore c++ exceptions

[nvptx] Ignore c++ exceptions

The nvptx port can't support exceptions using sjlj, because ptx does not
support sjlj.  However, default_except_unwind_info still returns UI_SJLJ, even
even if we configure with --disable-sjlj-exceptions, because UI_SJLJ is the
fallback option.

The reason default_except_unwind_info doesn't return UI_DWARF2 is because
DWARF2_UNWIND_INFO is not defined in defaults.h, because
INCOMING_RETURN_ADDR_RTX is not defined, because there's no ptx equivalent.

Testcase libgomp.c++/for-15.C currently doesn't compile unless fno-exceptions
is added because:
- it tries to generate sjlj exception handling code, and
- it tries to generate exception tables using label-addressed .byte sequence.
  Ptx doesn't support generating random data at a label, nor being able to
  load/write data relative to a label.

This patch fixes the first problem by using UI_TARGET for nvptx.

The second problem is worked around by generating all .byte sequences commented
out.  It would be better to have a narrower workaround, and define
TARGET_ASM_BYTE_OP to "error: .byte unsupported " or some such.

This patch does not enable exceptions for nvptx, it merely allows c++ programs
to run correctly if they do no use exception handling.

Build and reg-tested on x86_64 with nvptx accelerator.

2018-08-02  Tom de Vries  <tdevries@suse.de>

	PR target/86660
	* common/config/nvptx/nvptx-common.c (nvptx_except_unwind_info): New
	function.  Return UI_TARGET unconditionally.
	(TARGET_EXCEPT_UNWIND_INFO): Redefine to nvptx_except_unwind_info.
	* config/nvptx/nvptx.c (TARGET_ASM_BYTE_OP): Emit commented out '.byte'.

	* testsuite/libgomp.oacc-c++/routine-1-auto.C: Remove -fno-exceptions.
	* testsuite/libgomp.oacc-c++/routine-1-template-auto.C: Same.
	* testsuite/libgomp.oacc-c++/routine-1-template-trailing-return-type.C:
	Same.
	* testsuite/libgomp.oacc-c++/routine-1-template.C: Same.
	* testsuite/libgomp.oacc-c++/routine-1-trailing-return-type.C: Same.
	* testsuite/libgomp.oacc-c-c++-common/routine-1.c: Same.

From-SVN: r263265