PATCH: add missing __strdup decl to include/string.h

[Greg McGary]

Greg McGary <greg@kayak.mcgary.org> writes:

> ....  Without this patch, I get warnings about
> undeclared __strdup when building the BP lib.

I should add that this isn't simply a matter of compile-time warnings.
Without the decl, gcc has no way of knowing that __strdup has pointers
in its value+args signature, and so doesn't know to prepend "__BP_" to
its ASSEMBLER_NAME, so it generates calls to unbounded __strdup which
go undefined at link time.