Configure, DLL_EXPORT, and why --enable-shared fails on Cygwin

[Torbjorn Granlund]

<librik at panix.com> writes:

  So I can see two possibilities:
  
  (1) x86-defs.m4 should be using some other macro to
  detect a Cygwin DLL build.  (But I don't see anything
  else useful in the gcc command line, above.)
  
  (2) It was a mistake to remove -DDLL_EXPORT from the
  command line constructed in libtool by configure.
  
As it turns out, this GMP change was due to a change in libtool.m4,
committed to libtool 1.5.x.  Unfortunately, I the author of this
change forgot to make a change log entry, so I cannot track it.

I am not very familiar with the auto* stuff or libtool.  Perhaps
somebody on this list knows it better, and can take it from here?

The change was that they in AC_LIBTOOL_PROG_COMPILER_PIC moved cygwin*
from the same pattern where mingw* is, to the same pattern where irix
and osf are.

I am not saying that the change is incorrect.  Without a change log
entry one cannot tell.

  Can the developers for the GMP 4.2 build system suggest what the
  right solution should be?
  
I am preparing 4.2.1 and for that release, I crudely patched our
libtool.m4 to undo the problematic change.  A downside of that
approach is that things will break the day we install a newer libtool.

-- 
Torbjörn