pkg-config --cflags --libs "libxml-2.0 > 2.6.17" ならパスがでますが pkg-config --cflags --libs "libxml-2.0 > 2.6.17" -I/usr/include/libxml2 -lxml2 $ pkg-config --cflags libxml2 では出ないですね

Package libxml2 was not found in the pkg-config search path. Perhaps you should add the directory containing `libxml2.pc' to the PKG_CONFIG_PATH environment variable

(edited)