[Bug target/117854] gcc/config/nvptx/gen-opt.sh contains a bashism, causing build failure with /bin/sh as dash

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117854

--- Comment #3 from Sam James <sjames at gcc dot gnu.org> ---
Ditto gen-h.sh.