Replace rawmemchr (s, '\0') with strchr

Almost all uses of rawmemchr find the end of a string.  Since most targets use
a generic implementation, replacing it with strchr is better since that is
optimized by compilers into strlen (s) + s.  Also fix the generic rawmemchr
implementation to use a cast to unsigned char in the if statement.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

nss/nss_db/db-XXX.c

@@ -269,7 +269,7 @@ CONCAT(_nss_db_get,ENTNAME_r) (struct STRUCTURE *result, char *buffer,
 			       + state.header->valstrlen);
       while (entidx < end)
 	{
-	  const char *next = rawmemchr (entidx, '\0') + 1;
+	  const char *next = strchr (entidx, '\0') + 1;
 	  size_t len = next - entidx;
 
 	  if (len > buflen)