Validate digits of binary/octal constants

[ehaas]

Error message for invalid binary/octal constants could be improved:

int x = 0b19;
int y = 019;

clang output:

test.c:1:12: error: invalid digit '9' in binary constant
int x = 0b19;
           ^
test.c:2:11: error: invalid digit '9' in octal constant
int y = 019;
          ^

vs arocc

./test.c:1:12: error: expected ';', found 'an integer literal'
int x = 0b19;
           ^
./test.c:2:11: error: expected ';', found 'an integer literal'
int y = 019;
          ^