* compiler: extract c_common_macros from c_headers, and use it in bare_c_headers too. Support for ptr_str and string concatenation in -freestanding mode.
* Add tests for structs and string concatenation in -freestanding mode .
* Move check_string_add_works to string/string.v .
Added more array support that depends on malloc. Added string clone (that uses malloc). Added test for it. Eliminated stack allocated buffers from most of the unit checks.
Fixed exit for freestanding (as assert now uses it).
Running each function check now in a forked process so they can be killed or return other exit codes (and so each function runs, even if others crash)
