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/testlib/testrunner.c

@@ -101,7 +101,8 @@ static void TearDownTmpDir(void) {
 /**
  * Runs all test case functions in sorted order.
  */
-void testlib_runtestcases(testfn_t *start, testfn_t *end, testfn_t warmup) {
+void testlib_runtestcases(const testfn_t *start, const testfn_t *end,
+                          testfn_t warmup) {
   // getpid() calls are inserted to help visually see tests in traces
   // which can be performed on Linux, FreeBSD, OpenBSD, and XNU:
   //