Automatically disable 16-bit support in the PE build.

diff --git a/configure.ac b/configure.ac
index 76a56c8..ef835ea 100644
--- a/configure.ac
+++ b/configure.ac
@@ -848,6 +848,9 @@
       LIBEXT="dll"
     fi
     IMPLIBEXT="a"
+    dnl We can't build 16-bit NE dlls
+    WIN16_FILES=""
+    WIN16_INSTALL=""
     ;;
   *)
     AC_CHECK_HEADERS(dlfcn.h,