SYS funcs and GCC12 fixes (#1186)

* SYS functions and GCC 12 fixes

* Add implementation of _gettimeofday and settimeofday, _times
* Remove some GCC warnings about unimplemented SYS functions (e.g. _open) by making weak implementations that return errors.
* Removed _exit from crt0.S since we have a weak version in runtime.c and we don't want two weak impls since the linker can't pick. If the user omits runtime.c then they'll need to provide _exit or get the error
* Add sys/time.h to arch/cc.h for lwIP as it seems under GCC12 this is not getting included

src/rp2_common/pico_lwip/include/arch/cc.h

@@ -32,6 +32,8 @@
 #ifndef __CC_H__
 #define __CC_H__
 
+#include <sys/time.h>
+
 #if NO_SYS
 // todo really we should just not allow SYS_LIGHTWEIGHT_PROT for nosys mode (it doesn't do anything anyway)
 typedef int sys_prot_t;