Make more fixes and improvements

- Remove PAGESIZE constant
- Fix realloc() documentation
- Fix ttyname_r() error reporting
- Make forking more reliable on Windows
- Make execvp() a few microseconds faster
- Make system() a few microseconds faster
- Tighten up the socket-related magic numbers
- Loosen restrictions on mmap() offset alignment
- Improve GetProgramExecutableName() with getenv("_")
- Use mkstemp() as basis for mktemp(), tmpfile(), tmpfd()
- Fix flakes in pthread_cancel_test, unix_test, fork_test
- Fix recently introduced futex stack overflow regression
- Let sockets be passed as stdio to subprocesses on Windows
- Improve security of bind() on Windows w/ SO_EXCLUSIVEADDRUSE

third_party/chibicc/chibicc.main.c

@@ -1,7 +1,6 @@
-#include "libc/mem/arena.h"
+#include "third_party/chibicc/chibicc.h"
 #include "libc/runtime/internal.h"
 #include "libc/x/x.h"
-#include "third_party/chibicc/chibicc.h"
 #include "tool/build/lib/getargs.h"
 
 int main(int argc, char **argv) {