stack-protector configure test and MIPS64

[Roland McGrath]

> I'm not aware of any distribution compilers with that property, and this 
> test is really about working well with known distribution compilers (we 
> don't try to allow for every possible strange way a compiler could be 
> configured, just those that seem likely to arise in practice).  A false 
> negative would simply mean a build failure at some later point rather than 
> at configure time; I'm not convinced it's worth complicating this test to 
> avoid that for a hypothetical compiler.

Fair enough.