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.

test/libc/calls/commandv_test.c

@@ -45,7 +45,6 @@ void SetUpOnce(void) {
 }
 
 void SetUp(void) {
-  static int x;
   mkdir("bin", 0755);
   mkdir("home", 0755);
   oldpath = strdup(nulltoempty(getenv("PATH")));