[Bug libgomp/82864] Stop using GOMP_OFFLOAD_openacc_async_set_async

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82864

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
Hmm, I found this on openacc-gcc-7-branch:
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commit cd69c58db3f41ac72c20bc9b780772ab7e0c113e
Author: Chung-Lin Tang <cltang@codesourcery.com>
Date:   Tue Jul 25 15:02:26 2017 +0000

    OpenACC async re-work

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        libgomp/
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        (GOMP_OFFLOAD_openacc_async_set_async): Remove.
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