Fix -Wunterminated-string-initialization warning

Unbreaks the Cygwin build.

cutils.c

@@ -590,7 +590,13 @@ size_t utf8_encode_buf16(char *dest, size_t dest_len, const uint16_t *src, size_
  */
 
 /* 2 <= base <= 36 */
-char const digits36[36] = "0123456789abcdefghijklmnopqrstuvwxyz";
+char const digits36[36] = {
+    '0','1','2','3','4','5','6','7','8','9',
+    'a','b','c','d','e','f','g','h','i','j',
+    'k','l','m','n','o','p','q','r','s','t',
+    'u','v','w','x','y','z'
+};
+
 
 #define USE_SPECIAL_RADIX_10  1  // special case base 10 radix conversions
 #define USE_SINGLE_CASE_FAST  1  // special case single digit numbers

tests/test_conv.c

@@ -133,7 +133,12 @@ size_t i64toa_radix(char buf[minimum_length(66)], int64_t n, unsigned base);
  */
 
 /* 2 <= base <= 36 */
-char const digits36[36] = "0123456789abcdefghijklmnopqrstuvwxyz";
+char const digits36[36] = {
+    '0','1','2','3','4','5','6','7','8','9',
+    'a','b','c','d','e','f','g','h','i','j',
+    'k','l','m','n','o','p','q','r','s','t',
+    'u','v','w','x','y','z'
+};
 
 /*---- variants ----*/