Use DLL_EXPORT only on win

configure.ac

@@ -5636,9 +5636,11 @@ dnl Pic and shared libvlc stuff
 dnl
 AS_IF([test "${SYS}" = "mingw32" || test "${enable_libtool}" != "no"], [
   AC_DEFINE(HAVE_SHARED_LIBVLC, 1, [Define to 1 if libvlc is built as a shared library.])
-  FILE_LIBVLC_DLL="!define LIBVLC_DLL libvlc.dll"
   VLC_ADD_PLUGINS([${BUILTINS}])
-  VLC_ADD_CPPFLAGS([libvlc],[-DDLL_EXPORT])
+  AS_IF([test "${SYS}" = "mingw32"], [
+    FILE_LIBVLC_DLL="!define LIBVLC_DLL libvlc.dll"
+    VLC_ADD_CPPFLAGS([libvlc],[-DDLL_EXPORT])
+  ])
   BUILTINS=""
 ], [
   LDFLAGS_vlc="${LDFLAGS_vlc} ${LDFLAGS_libvlc}"