Make more libc improvements

- Make memmem() faster
- Make readdir() thread safe
- Remove 64kb limit from mkdeps.com
- Add old crypt() function from Musl
- Improve new fix-third-party.py tool
- Improve libc/isystem/ headers and fix bugs

libc/log/log.h

@@ -41,7 +41,6 @@ COSMOPOLITAN_C_START_
 
 extern FILE *__log_file;
 
-void perror(const char *) relegated;   /* print the last system error */
 void __die(void) relegated wontreturn; /* print backtrace and abort() */
 void meminfo(int);                     /* shows malloc statistics &c. */
 void memsummary(int);                  /* light version of same thing */