Silence Appveyor's VC compilation warnings.

mrbgems/mruby-pack/src/pack.c

@@ -64,7 +64,7 @@ static int littleendian = 0;
 
 const static unsigned char base64chars[] =
     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
-static signed char base64_dec_tab[128];
+static unsigned char base64_dec_tab[128];
 
 
 static int

mrbgems/mruby-sleep/src/mrb_sleep.c

@@ -29,7 +29,7 @@
 #ifdef _WIN32
     #include <windows.h>
     #define sleep(x) Sleep(x * 1000)
-    #define usleep(x) Sleep(((x)<1000) ? 1 : ((x)/1000))
+    #define usleep(x) Sleep((DWORD)((x)<1000) ? 1 : ((x)/1000))
 #else
     #include <unistd.h>
     #include <sys/time.h>

mrbgems/mruby-string-ext/src/string.c

@@ -279,7 +279,7 @@ static struct tr_pattern*
 tr_parse_pattern(mrb_state *mrb, struct tr_pattern *ret, const mrb_value v_pattern, mrb_bool flag_reverse_enable)
 {
   const char *pattern = RSTRING_PTR(v_pattern);
-  int pattern_length = RSTRING_LEN(v_pattern);
+  mrb_int pattern_length = RSTRING_LEN(v_pattern);
   mrb_bool flag_reverse = FALSE;
   struct tr_pattern *pat1;
   int i = 0;
@@ -438,7 +438,8 @@ str_tr(mrb_state *mrb, mrb_value str, mrb_value p1, mrb_value p2, mrb_bool squee
           mrb_raisef(mrb, E_ARGUMENT_ERROR, "character (%S) out of range",
                      mrb_fixnum_value((mrb_int)c));
         }
-	lastch = s[i] = c;
+	lastch = c;
+	s[i] = (char)c;
       }
     }
   }

src/vm.c

@@ -186,7 +186,7 @@ stack_extend_alloc(mrb_state *mrb, mrb_int room)
 
   if (off > size) size = off;
 #ifdef MRB_STACK_EXTEND_DOUBLING
-  if (room <= (size_t)size)
+  if ((size_t)room <= size)
     size *= 2;
   else
     size += room;