[Bug target/86800] nvptx port needs updating for CVE-2017-5753

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86800

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
Hmm, at https://nvidia.custhelp.com/app/answers/detail/a_id/4610 I read:
...
NVIDIA GeForce Experience (GFE) response to CPU speculative side channel
vulnerabilities - CVE-2017-5753, CVE-2017-5715, CVE-2017-5754
Bulletin Summary

  ...

NVIDIA believes our GPU hardware is immune to the reported security issue.
...

So I think we can define this, and be done with it:
...
#undef TARGET_HAVE_SPECULATION_SAFE_VALUE
#define TARGET_HAVE_SPECULATION_SAFE_VALUE speculation_safe_value_not_needed.
...