tests: update some tests to pass on Mac

Signed-off-by: Jean Privat <jean@pryen.org>
c_src: update Makefile to compile on MacOSX

Add a make variable OLDNITCOPT to give options for the first step

Signed-off-by: Jean Privat <jean@pryen.org>
mkcsrc: clear OLDNITCOPT in src/Makefile

Signed-off-by: Jean Privat <jean@pryen.org>