Fix warnings

This change fixes Cosmopolitan so it has fewer opinions about compiler
warnings. The whole repository had to be cleaned up to be buildable in
-Werror -Wall mode. This lets us benefit from things like strict const
checking. Some actual bugs might have been caught too.

libc/calls/fstatfs-nt.c

@@ -37,7 +37,6 @@
 textwindows int sys_fstatfs_nt(int64_t handle, struct statfs *f) {
   uint64_t w;
   NtStatus st;
-  uint32_t type;
   uint32_t h, i, j;
   struct NtIoStatusBlock io;
   struct NtFileFsFullSizeInformation fs;