[Bug target/96932] [nvptx] atomic_exchange missing barrier

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96932

--- Comment #5 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 50811
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50811&action=edit
Tentative patch