Make sure bundled tinyxml is ahead of system tinyxml in search path

Index: src/base/tinyxml/Makefile.am
--- src/base/tinyxml/Makefile.am.orig
+++ src/base/tinyxml/Makefile.am
@@ -1,7 +1,8 @@
 AM_CPPFLAGS = $(WX_CXXFLAGS) \
 				-I$(top_srcdir)/src/sdk/wxscintilla/include \
 				-I$(top_srcdir)/src/include \
-				-I$(top_srcdir)/src/include/tinyxml
+				-I$(top_srcdir)/src/include/tinyxml \
+				$(WX_CXXFLAGS)
 
 noinst_LTLIBRARIES = libtinyxml.la