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.

examples/crashreport2.c

@@ -43,7 +43,6 @@
  */
 
 int main(int argc, char *argv[]) {
-  volatile int64_t x;
   ShowCrashReports();
   printf("please press ctrl+\\ and see what happens...\n");
   sigsuspend(0);