* 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.