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/ftrace_install.c

@@ -18,14 +18,13 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/fmt/itoa.h"
 #include "libc/intrin/kprintf.h"
+#include "libc/runtime/internal.h"
 #include "libc/runtime/runtime.h"
 #include "libc/runtime/stack.h"
 #include "libc/runtime/symbols.internal.h"
 
 void ftrace_hook(void);
 
-_Hide int ftrace_stackdigs;
-
 textstartup int ftrace_install(void) {
   if (GetSymbolTable()) {
     ftrace_stackdigs = LengthInt64Thousands(GetStackSize());