fix: correct strtol0x signature

Building with older compilers, such as Xcode's gcc 4.2,
triggered "different width due to prototype" warnings.

This occurs because character literals (e.g., 'X') are
promoted to `int` when passed as function arguments, but
the `strtol0X` function signature expected a `char`.

This change corrects the function signature to accept an
`int`, which resolves the compiler warnings and improves
portability.

Author: tomghuang

src/arg_int.c

@@ -56,7 +56,7 @@ static void arg_int_resetfn(void* parent_) {
 /* eg: to parse oct str="+0o12324", specify X='O' and base=8.       */
 /* eg: to parse bin str="-0B01010", specify X='B' and base=2.       */
 /* Failure of conversion is indicated by result where *endptr==str. */
-static long int strtol0X(const char* str, const char** endptr, char X, int base) {
+static long int strtol0X(const char* str, const char** endptr, int X, int base) {
     long int val;          /* stores result */
     int s = 1;             /* sign is +1 or -1 */
     const char* ptr = str; /* ptr to current position in str */