Mark _resumecontext as dead. ANSIfy all declarations for it.

Remove clause 3 and 4 from TNF licenses

Pull over rev. 1.5 of the i386 version (../../i386/resumecontext.S),
quoting Matthias Drochner:

> -check for a NULL uc_link before calling setcontext(2); do a real exit(3)
> instead with exit handl

Pull over rev. 1.5 of the i386 version (../../i386/resumecontext.S),
quoting Matthias Drochner:

> -check for a NULL uc_link before calling setcontext(2); do a real exit(3)
> instead with exit handlers and all that
> -If setcontext(2) returns (which it shouldn't), do an _exit(-1) rather
> than relying on a sensible return value to use as exit code. Makes
> it less likely that an ucontext corruption goes unnoticed.

This also fixes regress/lib/libc/context for sparc64.

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Merge the nathanw_sa branch.