Improve cosmo's conformance to libc-test

This change addresses various open source compatibility issues, so that
we pass 313/411 of the tests in https://github.com/jart/libc-test where
earlier today we were passing about 30/411 of them, due to header toil.
Please note that Glibc only passes 341/411 so 313 today is pretty good!

- Make the conformance of libc/isystem/ headers nearly perfect
- Import more of the remaining math library routines from Musl
- Fix inconsistencies with type signatures of calls like umask
- Write tests for getpriority/setpriority which work great now
- conform to `struct sockaddr *` on remaining socket functions
- Import a bunch of uninteresting stdlib functions e.g. rand48
- Introduce readdir_r, scandir, pthread_kill, sigsetjmp, etc..

Follow the instructions in our `tool/scripts/cosmocc` toolchain to run
these tests yourself. You use `make CC=cosmocc` on the test repository

libc/isystem/stdio.h

@@ -1,9 +1,11 @@
 #ifndef LIBC_ISYSTEM_STDIO_H_
 #define LIBC_ISYSTEM_STDIO_H_
 #include "libc/calls/calls.h"
+#include "libc/calls/dprintf.h"
+#include "libc/calls/weirdtypes.h"
 #include "libc/fmt/fmt.h"
 #include "libc/mem/fmt.h"
-#include "libc/stdio/lock.internal.h"
 #include "libc/stdio/stdio.h"
 #include "libc/stdio/temp.h"
+#include "third_party/musl/tempnam.h"
 #endif