Use --disable-gdbserver in build-many-glibcs.py.

Use --disable-gdbserver in build-many-glibcs.py.

Now that binutils-gdb has gdbserver at top level, an extra
--disable-gdbserver configure option is needed when configuring
binutils from a git checkout to avoid it also building gdbserver
unnecessarily (although fairly harmlessly).  This patch updates the
options used in build-many-glibcs.py accordingly (although this might
end up not being needed depending on what happens regarding whether
gdbserver gets built for host != target).

Tested with a build-many-glibcs.py compilers build for
aarch64-linux-gnu using binutils-gdb master.