debug/gdb: correct compilation error when stpcpy is a define

On OSX stpcpy is a define which is not recognized by gdb's configure.
This results in a compilation error.

Reported-by: "Guylhem Aznar" <crossgcc@guylhem.net>
Signed-off-by: "Titus von Boxberg" <titus@v9g.de>

 reporter_name="Ioannis E. VENETIS"

 reporter_url="http://sourceware.org/ml/crossgcc/2009-11/msg00109.html"

 reporter_comment=""