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/intrin/strchr_test.c

@@ -72,7 +72,6 @@ TEST(strchrnul, notFound_returnsPointerToNulByte) {
 }
 
 char *strchr_pure(const char *s, int c) {
-  char *r;
   for (c &= 0xff;; ++s) {
     if ((*s & 0xff) == c) return (char *)s;
     if (!*s) return NULL;
@@ -108,7 +107,7 @@ BENCH(strchr, bench) {
 char *memchr_pure(const char *m, int c, size_t n) {
   const unsigned char *p, *pe;
   for (c &= 0xff, p = (const unsigned char *)m, pe = p + n; p < pe; ++p) {
-    if (*p == c) return p;
+    if (*p == c) return (void *)p;
   }
   return NULL;
 }
@@ -127,10 +126,9 @@ TEST(memchr, fuzz) {
 }
 
 char *strchrnul_pure(const char *s, int c) {
-  char *r;
   for (c &= 0xff;; ++s) {
     if ((*s & 0xff) == c) return (char *)s;
-    if (!*s) return s;
+    if (!*s) return (void *)s;
   }
 }
 
@@ -150,7 +148,7 @@ TEST(strchrnul, fuzz) {
 void *rawmemchr_pure(const void *m, int c) {
   const unsigned char *s;
   for (c &= 255, s = m;; ++s) {
-    if (*s == c) return s;
+    if (*s == c) return (void *)s;
   }
 }