[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 via Gcc-bugs]

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

--- Comment #1 from Sam James <sjames at gcc dot gnu.org> ---
Introduced by r12-7424-gd59d13c89503ba.