Include bundled header files before others. For example, this fixes build
with conflicting header files from graphics/jpeg. Note OTHER_INCLUDES or
OTHER_CPPFLAGS may be used instead. However, I think this is the least
intrusive change. Also, note java/openjdk6 already has a similar fix and
java/openjdk8 does not need it.
Tested by: Jonathan Chen (jonc at chen dot org dot nz)