newlib/configure.host: Turn off sti/cli for i386 setjmp for i386-rtems*

newlib/configure.host: Turn off sti/cli for i386 setjmp for i386-rtems*

When running RTEMS paravirtualized in user space, the cli/sti instructions
can't be used. But I can't see why they are needed in either user or
supervisor state. Turning the use of them off for RTEMS.

This code is unmodified since the beginning of the repository, so I have
no insight into why it was done. I may even have been the one to add them.
Absolutely no idea except they aren't necessary.