tell gcc where to look for includes needed to create switch_swigable_cpp.h, build fails otherwise

Makefile.am

@@ -253,8 +253,10 @@ $(top_builddir)/libfreeswitch_la-switch_console.lo: src/include/switch_version.h
 $(libfreeswitch_la_SOURCES): $(CORE_LIBS) $(switch_builddir)/quiet_libtool $(switch_builddir)/modules.conf  
 
 src/include/switch_swigable_cpp.h: $(switch_srcdir)/src/include/switch_cpp.h
-	$(CC) -E $(switch_srcdir)/src/include/switch_cpp.h -DSWITCH_DECLARE_CLASS= -DSWITCH_DECLARE\(x\)=x -DSWITCH_DECLARE_CONSTRUCTOR= -DSWITCH_DECLARE_NONSTD\(x\)=x 2>/dev/null | grep -v "^#" > src/include/switch_swigable_cpp.h 
-
+	$(CC) -E $(switch_srcdir)/src/include/switch_cpp.h \
+		-I$(switch_srcdir)/src/include -I$(switch_srcdir)/libs/libteletone/src \
+		-DSWITCH_DECLARE_CLASS= -DSWITCH_DECLARE\(x\)=x -DSWITCH_DECLARE_CONSTRUCTOR= \
+		-DSWITCH_DECLARE_NONSTD\(x\)=x 2>/dev/null | grep -v "^#" > src/include/switch_swigable_cpp.h
 
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