[PATCH] Minor tweaks to libiberty's strdup

[DJ Delorie]

> Could you comment on Kaveh's recommendation that we should use
> ANSI_PROTOTYPES instead of __STDC__?
> http://gcc.gnu.org/ml/gcc-patches/2003-04/msg00963.html
> 
> I'm not sure of the issues, but I am happy to submit patches to
> standardize some of these features (size_t vs int for strlen etc...)
> once I know what's preferred.

ANSI_PROTOTYPES is preferred, but of course you need to include
ansidecl.h to get that.