* instead of /usr/include use the current SDK path as system
include directory (/usr/include is empty with current tools)
(this also removes the need to add these paths in individual
Makefiles)
* define _DARWIN_C_SOURCE in tcc.h to get the full set of decls
from system headers (e.g. vsnprintf), similar to _GNU_SOURCE
(and don't define _ANSI_SOURCE in the main Makefile anymore)
* tests/tests2/Makefile: remove the -w flag, it's added when necessary
in the rules generating the .expect files
4eff2b5f6a