Don't add a bogus C:/cygwin64/lib/x86 (or similar) directory to ILIB

If we don't know of any separate DirectX SDK library, don't use the
$DIRECTXSDK_LIB variable which is bogus at that point.

Thanks to Nicholas Ferguson for noticing.

Change-Id: I333478da7757694ca9236fd485e93bbd88305278

configure.ac

@@ -12830,7 +12830,7 @@ if test "$build_os" = "cygwin"; then
     fi
     ILIB="$ILIB;$DOTNET_FRAMEWORK_HOME/lib"
 
-    if test "$ENABLE_DIRECTX" = "TRUE"; then
+    if test "$ENABLE_DIRECTX" = "TRUE" -a "$HAVE_DIRECTXSDK_LIB" = "yes"; then
         ILIB="$ILIB;$DIRECTXSDK_LIB"
     fi
     AC_SUBST(ILIB)