cgen: fix maps with i32 keys

vlib/builtin/string.v

@@ -1488,6 +1488,24 @@ pub fn (s string) capitalize() string {
 	return res
 }
 
+// uncapitalize returns the string with the first character uncapitalized.
+// Example: assert 'Hello, Bob!'.uncapitalize() == 'hello, Bob!'
+[direct_array_access]
+pub fn (s string) uncapitalize() string {
+	if s.len == 0 {
+		return ''
+	}
+	s0 := s[0]
+	letter := s0.ascii_str()
+	uletter := letter.to_lower()
+	if s.len == 1 {
+		return uletter
+	}
+	srest := s[1..]
+	res := uletter + srest
+	return res
+}
+
 // is_capital returns `true`, if the first character in the string `s`,
 // is a capital letter, and the rest are NOT.
 // Example: assert 'Hello'.is_capital() == true

vlib/v/gen/c/cgen.v

@@ -3107,7 +3107,8 @@ fn (mut g Gen) map_fn_ptrs(key_typ ast.TypeSymbol) (string, string, string, stri
 			key_eq_fn = '&map_eq_int_2'
 			clone_fn = '&map_clone_int_2'
 		}
-		.int, .u32, .rune, .f32, .enum_ {
+		.int, .i32, .u32, .rune, .f32, .enum_ {
+			// XTODO i64
 			hash_fn = '&map_hash_int_4'
 			key_eq_fn = '&map_eq_int_4'
 			clone_fn = '&map_clone_int_4'
@@ -3132,7 +3133,7 @@ fn (mut g Gen) map_fn_ptrs(key_typ ast.TypeSymbol) (string, string, string, stri
 			free_fn = '&map_free_string'
 		}
 		else {
-			verror('map key type not supported')
+			verror('map key type `${key_typ.name}` not supported')
 		}
 	}
 	return hash_fn, key_eq_fn, clone_fn, free_fn