AC_LIBTOOL_WIN32_DLL for libgfortran

[FX Coudert]

> Did you put it in the toplevel configure.in or in
> libgfortran/configure.ac?  I suspect it needs to be in the former,
> because the latter probably shares the same config.cache and thus it
> won't be checked a second time when running configure for libgfortran.

Tried to put it into the toplevel configure.ac, but there is no  
AC_PROG_LIBTOOL there, so I put it somewhere near other AC_ macros  
(see patch below). Autoconf then says:

$ autoconf
configure.ac:1071: error: possibly undefined macro: AC_LIBTOOL_WIN32_DLL
       If this token and others are legitimate, please use  
m4_pattern_allow.
       See the Autoconf documentation.


Index: configure.ac
===================================================================
--- configure.ac        (revision 122655)
+++ configure.ac        (working copy)
@@ -1068,6 +1068,8 @@
    fi
fi
+AC_LIBTOOL_WIN32_DLL
+
ACX_PROG_GNAT
ACX_PROG_CMP_IGNORE_INITIAL