Conflicting declarations of variable scheme_thread_locals

[David Bremner]

A debian user reported the following potential undefined behaviour in
Racket 6.5:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=702859

Unfortunately I don't have the tooling to easily check if this still
present, but maybe you can tell just by looking.

[Matthew Flatt]

Thanks for forwarding the report! I think this is fixed in v6.9, since
"gmp.c" is now compiled with `MZ_PRECISE_GC` instead of trying to use
the non-`MZ_PRECISE_GC` object.

https://github.com/racket/racket/commit/5a4391dd90066e5485773d7832a65c6a59a8aa8c