Fix sysdeps/mips/__longjmp.c warning

[Rich Felker]

On Wed, Nov 26, 2014 at 04:34:50PM +0000, Joseph Myers wrote:
> This patch fixes
> 
> .../sysdeps/mips/__longjmp.c:27:1: warning: function declaration isn't a prototype [-Wstrict-prototypes]
> 
> which arose I think from the MIPS16 changes (renaming the function to
> ____longjmp with an alias __longjmp, so a prior header prototype for
> __longjmp no longer sufficed to prevent a warning).  I've made the
> function use a prototype definition, which is what we want for all
> function definitions in glibc anyway.
> 
> Tested for MIPS and committed.

This file is utter nonsense and really needs to be replaced completely
by either one giant __asm__ block or a .S file. As-written, it assumes
the compiler will not use or clobber any registers between one asm
statement and the next, which is an invalid assumption. setjmp_aux.c
is even worse and relies on the same invalid assumption and on tail
call optimization.

Rich