Build fix for tinyxml

The recipe used to download a CMakeLists.txt that's no longer available.
Instead I added the makefile from Gentoo [1], as suggested by PulkoMandy,
which I slightly changed to save the need to patch it.

dev-libs/tinyxml/additional-files/Makefile

@@ -0,0 +1,44 @@
+AR ?= ar
+CXX ?= g++
+CXXFLAGS += -Wall
+RANLIB ?= ranlib
+LIBDIR ?= /usr/lib
+
+name = libtinyxml
+major = @MAJOR_V@
+minor = @MINOR_V@
+version = $(major).$(minor)
+
+src = tinyxml.cpp tinyxmlparser.cpp tinyxmlerror.cpp tinystr.cpp
+lo = $(addsuffix .lo,$(basename ${src}))
+o = $(addsuffix .o,$(basename ${src}))
+
+lib = so
+ifeq ($(shell uname),Darwin)
+	lib = dylib
+endif
+
+all: $(name).a $(name).$(lib)
+
+%.o: %.cpp
+	$(CXX) -c $(CXXFLAGS) $(CPPFLAGS) $< -o $@
+
+$(name).a: $(o)
+	$(AR) rc $(name).a $(o)
+	$(RANLIB) $(name).a
+
+%.lo: %.cpp
+	$(CXX) -c $(CXXFLAGS) $(CPPFLAGS) -fPIC $< -o $@
+
+$(name).so: $(lo)
+	$(CXX) $(LDFLAGS) -fPIC -shared $(lo) -Wl,-soname,$(name).so.$(major) -o $(name).so.$(version)
+	ln -s $(name).so.$(version) $(name).so.$(major)
+	ln -s $(name).so.$(version) $(name).so
+
+$(name).dylib: $(lo)
+	$(CXX) $(LDFLAGS) -fPIC -dynamiclib $(lo) -install_name $(LIBDIR)/$(name).$(major).dylib -o $(name).$(version).dylib
+	ln -s $(name).$(version).dylib $(name).$(major).dylib
+	ln -s $(name).$(version).dylib $(name).dylib
+
+clean:
+	-rm -f *.o *.lo *.so* *.a