[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 #2 from Sam James <sjames at gcc dot gnu.org> ---
(In reply to Sam James from comment #0)
> Please either change the script to have a bash shebang or fix the bashism.

shebang won't work as it's invoked with $(SHELL).