libxmlpp: need BR2_USE_MMU dependancy

Fixes:
  http://autobuild.buildroot.org/results/d4d/d4d10ddccf4f53087e2012a36fd80808f7dc7cc5/

Signed-off-by: Ryan Barnett <rjbarnet@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libxmlpp/Config.in

@@ -5,6 +5,7 @@ config BR2_PACKAGE_LIBXMLPP
 	depends on BR2_INSTALL_LIBSTDCPP
 	depends on BR2_USE_WCHAR # glibmm -> libglib2
 	depends on BR2_TOOLCHAIN_HAS_THREADS # glibmm -> libglib2
+	depends on BR2_USE_MMU # glibmm -> libglib2
 	help
 	  libxml++ is a C++ wrapper for the libxml XML parser library.