Make fixes and improvements

- Fix handling of precision in hex float formatting
- Enhance the cocmd interpreter for system() and popen()
- Manually ran the Lua unit tests, which are now passing
- Let stdio i/o operations happen when file is in error state
- We're now saving and restoring xmm in ftrace out of paranoia

libc/runtime/runtime.h

@@ -114,8 +114,6 @@ void _Exitr(int) libcesque wontreturn;
 void _Exit1(int) libcesque wontreturn;
 void _restorewintty(void);
 void __paginate(int, const char *);
-void _loadxmm(void *);
-void _savexmm(void *);
 long _missingno();
 /* memory management */
 void _weakfree(void *);