Removed the unsafe nxt_memchr() wrapper for memchr(3).

The casts are unnecessary, since memchr(3)'s argument is 'const void *'.
It might have been necessary in the times of K&R, where 'void *' didn't
exist.  Nowadays, it's unnecessary, and _very_ unsafe, since casts can
hide all classes of bugs by silencing most compiler warnings.

The changes from nxt_memchr() to memchr(3) were scripted:

$ find src/ -type f \
  | grep '\.[ch]$' \
  | xargs sed -i 's/nxt_memchr/memchr/'

Reviewed-by: Andrew Clayton <a.clayton@nginx.com>
Signed-off-by: Alejandro Colomar <alx@nginx.com>

src/nxt_http_route.c

@@ -1016,7 +1016,7 @@ nxt_http_route_pattern_create(nxt_task_t *task, nxt_mp_t *mp,
     if (type == NXT_HTTP_ROUTE_PATTERN_EXACT) {
         tmp.start = test.start;
 
-        p = nxt_memchr(test.start, '*', test.length);
+        p = memchr(test.start, '*', test.length);
 
         if (p == NULL) {
             /* No '*' found - EXACT pattern. */
@@ -1414,7 +1414,7 @@ nxt_http_pass_segments(nxt_mp_t *mp, nxt_str_t *pass, nxt_str_t *segments,
     nxt_memzero(segments, n * sizeof(nxt_str_t));
 
     do {
-        p = nxt_memchr(rest.start, '/', rest.length);
+        p = memchr(rest.start, '/', rest.length);
 
         if (p != NULL) {
             n--;