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/stdio/vappendf_test.c

@@ -171,7 +171,6 @@ TEST(appendd, nontrivialAmountOfMemory) {
 }
 
 BENCH(vappendf, bench) {
-  const char t[] = {0};
   char *b = 0;
   EZBENCH2("appendf", donothing, appendf(&b, "hello"));
   EZBENCH2("kappendf", donothing, kappendf(&b, "hello"));