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

tool/build/lib/syscall.c

@@ -40,13 +40,14 @@
 #include "libc/log/check.h"
 #include "libc/log/log.h"
 #include "libc/macros.internal.h"
+#include "libc/mem/gc.internal.h"
 #include "libc/mem/mem.h"
 #include "libc/nexgen32e/vendor.internal.h"
-#include "libc/mem/gc.internal.h"
 #include "libc/runtime/pc.internal.h"
 #include "libc/runtime/runtime.h"
 #include "libc/sock/select.h"
 #include "libc/sock/sock.h"
+#include "libc/sock/struct/sockaddr.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/af.h"
 #include "libc/sysv/consts/at.h"
@@ -485,7 +486,7 @@ static int OpAccept4(struct Machine *m, int fd, int64_t aa, int64_t asa,
 }
 
 static int OpConnectBind(struct Machine *m, int fd, int64_t aa, uint32_t as,
-                         int impl(int, const void *, uint32_t)) {
+                         int impl(int, const struct sockaddr *, uint32_t)) {
   struct sockaddr_in addr;
   struct sockaddr_in_bits gaddr;
   if (as != sizeof(gaddr)) return einval();
@@ -540,7 +541,7 @@ static int OpGetsockopt(struct Machine *m, int fd, int level, int optname,
 }
 
 static int OpSocketName(struct Machine *m, int fd, int64_t aa, int64_t asa,
-                        int SocketName(int, void *, socklen_t *)) {
+                        int SocketName(int, struct sockaddr *, socklen_t *)) {
   int rc;
   uint32_t addrsize;
   uint8_t gaddrsize[4];