--enable-auto-image-base linker option for Cygwin

[James R. Phillips]

Cygwin maintainers periodically grouse about needing the rebase utility, and
recently have proposed use of --enable-auto-image-base as a linker option, in
the hopes of reducing or eliminating dll address base collisions, thus
eliminating the need for rebase.

AFAICT, this would require adding "-wl,--enable-auto-image-base" to the
SH_LDFLAGS defined for cygwin/mingw in configure.in.

Is this feasible, and is it worth doing?

I have not seen the "failing fork()" issue that necessitates use of rebase with
the cygwin build 2.1.71-1.  I have seen it in the past, though, for earlier
builds that were not official cygwin packages.