get rid of some compiler warnings

fmt/fmt_longlong.c

@@ -3,7 +3,7 @@
 size_t fmt_longlong(char *dest,signed long long int i) {
   if (i<0) {
     if (dest) *dest++='-';
-    return fmt_ulonglong(dest,-i)+1;
+    return fmt_ulonglong(dest,(unsigned long long)-i)+1;
   } else
-    return fmt_ulonglong(dest,i);
+    return fmt_ulonglong(dest,(unsigned long long)i);
 }

fmt/fmt_str.c

@@ -9,5 +9,5 @@ size_t fmt_str(char *out,const char *in) {
     if (!*t) break; if (s) { *s=*t; ++s; } ++t;
     if (!*t) break; if (s) { *s=*t; ++s; } ++t;
   }
-  return t-in;
+  return (size_t)(t-in);
 }

fmt/fmt_utf8.c

@@ -3,7 +3,7 @@
 size_t fmt_utf8(char *dest,uint32_t n) {
   size_t i,j;
   if (n<=0x7f) {
-    if (dest) *dest=n;
+    if (dest) *dest=(char)n;
     return 1;
   }
   for (i=0x3f,j=1; i<0x7fffffff; i=(i<<5)|0x1f, ++j) {
@@ -11,9 +11,9 @@ size_t fmt_utf8(char *dest,uint32_t n) {
       --j;
       if (dest) {
 	size_t k=j*6;
-	*dest++=((char)0xc0 >> (j-1)) | (n >> k);
+	*dest++=(char)(((char)0xc0 >> (j-1)) | (char)(n >> k));
 	while (k) {
-	  *dest++=0x80 | ((n >> (k-6)) & 0x3f);
+	  *dest++=(char)(0x80 | ((n >> (k-6)) & 0x3f));
 	  k-=6;
 	}
       }