Don't include <crypt.h> from <stdlib.h>

[dfyz]

This PR tries to re-land #1104, which was closed because I had tried to make a PR directly from my master and messed up.
Except for the branch name, this PR is identical to #1104, so I'm copying the original PR description below verbatim.

POSIX says that crypt() resides in <unistd.h>. As far as I know, crypt() doesn't have anything to do with the C standard library, so including it unconditionally from <stdlib.h> is somewhat strange and breaks the build of the Lua MD5 implementation bundled with LuaTeX:

/home/dfyz/busytex/source/texlive/texk/web2c/luatexdir/luamd5/md5lib.c:117:12: error: conflicting types for ‘crypt’; have ‘int(lua_State *)’
  117 | static int crypt (lua_State *L) {
      |            ^~~~~
In file included from /home/dfyz/cosmopolitan/cosmocc/include/stdlib.h:17,
                 from /home/dfyz/busytex/source/texlive/texk/web2c/luatexdir/luamd5/md5lib.c:8:
/home/dfyz/cosmopolitan/cosmocc/include/third_party/musl/crypt.h:12:7: note: previous declaration of ‘crypt’ with type ‘char *(const char *, const char *)’
   12 | char *crypt(const char *, const char *);
      |       ^~~~~

A simpler test program is just:

#include <stdlib.h>

void crypt() {
}

int main() {
}

It builds successfully with both gcc (glibc) and musl-gcc (musl), but fails to build with cosmocc (with an error very similar to the above).
Given that crypt() is a very short word and is likely to clash with other real-world programs in the future, I suggest removing this include.

[jart]

Looks like this happened due to setkey(). I'll write a follow-up change to put that back into stdlib.h after merging this. Thanks!