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/backtrace2.c

@@ -120,18 +120,16 @@ static int PrintBacktraceUsingAddr2line(int fd, const struct StackFrame *bp) {
     j += uint64toarray_radix16(addr - 1, buf + j) + 1;
   }
   argv[i++] = NULL;
-  if (sys_pipe(pipefds) == -1) {
+  if (sys_pipe2(pipefds, O_CLOEXEC) == -1) {
     return -1;
   }
-  if ((pid = vfork()) == -1) {
+  if ((pid = fork()) == -1) {
     sys_close(pipefds[0]);
     sys_close(pipefds[1]);
     return -1;
   }
   if (!pid) {
     sys_dup2(pipefds[1], 1);
-    if (pipefds[0] != 1) sys_close(pipefds[0]);
-    if (pipefds[1] != 1) sys_close(pipefds[1]);
     sys_execve(addr2line, argv, environ);
     _Exit(127);
   }

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 */