configure.ac: Actually build dlls when cross-compiling with mingw32.

Original commit message from CVS:
Patch by: Damien Lespiau <damien dot lespiau at gmail dot com>
* configure.ac:
Actually build dlls when cross-compiling with mingw32.
Fixes bug #526247.

ChangeLog

+2008-04-06  Sebastian Dröge  <slomo@circular-chaos.org>
+
+	Patch by: Damien Lespiau <damien dot lespiau at gmail dot com>
+
+	* configure.ac:
+	Actually build dlls when cross-compiling with mingw32.
+	Fixes bug #526247.
+
 2008-04-03  Tim-Philipp Müller  <tim at centricular dot net>
 
 	* configure.ac:

configure.ac

@@ -51,6 +51,7 @@ dnl the generated libtool script has no support for the listed tags.
 dnl So this needs to be fixed first if we want to use this
 dnl AS_LIBTOOL_TAGS
 
+AC_LIBTOOL_WIN32_DLL
 AM_PROG_LIBTOOL
 
 dnl *** required versions of GStreamer stuff ***