add support for both system or local zlib

Signed-off-by: Cristian Stoica <crististm@gmail.com>
regenerate files after macro patches

Signed-off-by: Cristian Stoica <crististm@gmail.com>
zlib: consume config options

Signed-off-by: Cristian Stoica <crististm@gmail.com>
zlib: do not track volatile Makefile

Signed-off-by: Cristian Stoica <crististm@gmail.com>
Check for cxx11 support as reported by autoconf

Signed-off-by: Cristian Stoica <crististm@gmail.com>
add Readme for autotools maintainers

Signed-off-by: Cristian Stoica <crististm@gmail.com>