Do not build gdbserver with -Werror by default if development=false

On GDB release branches, we change $development in gdb/development.sh
to false, in order to build the GDB release without -Werror by default,
thus avoiding harmless compiler warnings from breaking the build of
someone who's only interested in building GDB rather than working
on it.

This patch implements the same strategy for gdbserver, using the exact
same method.

gdb/gdbserver/ChangeLog:

        * configure.ac: Only use -Werror by default when DEVELOPMENT
        is true.
        * configure: Regenerate.

Tested on x86_64-linux, by rebuilding GDBserver first with development
set to true, and then doing it again with development set to false.
Werror was used in the first case, but not in the second.