[Patch, MIPS] Modify memset.S for mips32r6/mips64r6

[Joseph Myers]

On Fri, 19 Dec 2014, Matthew Fortune wrote:

> > +#if __mips_isa_rev > 5
> 
> I've just so happened to be starting some mips2 tests with glibc
> and found see that __mips_isa_rev is not defined below mips32.
> This is then an error given -Werror is in force.

We still have -Wno-error=undef, so it *shouldn't* be an error (but once 
Siddhesh's remaining -Wundef fixes are in, and any further fixes needed to 
get clean for -Wundef in at least one configuration, we should remove 
-Wno-error=undef, so such issues certainly need fixing soon).

> i.e. I think we will need a defined(__mips_isa_rev) in any of the
> conditions which use it. This is likely to affect all of the R6
> patches.

Please put this in a central place (a single header that defines 
__mips_isa_rev to 0 if not already defined, for example) rather than 
duplicating "defined" tests in different places ("defined" tests are 
typo-prone and so discouraged in glibc).

-- 
Joseph S. Myers
joseph@codesourcery.com