Fix incorrect result of Math.abs() with char type

Math.abs() with char type may return incorrect result after C2 superword optimization. It can be reproduced by below Java code and commands.

public class Bug {
    private static int SIZE = 60000;
    private static char[] a = new char[SIZE];
    private static char[] b = new char[SIZE];

    public static void main(String[] args) {
        for (int i = 0; i < SIZE; i++) {
            a[i] = b[i] = (char) i;
        }
        for (int i = 0; i < SIZE; i++) {
            a[i] = (char) Math.abs(a[i]);
        }
        for (int i = 0; i < SIZE; i++) {
            if (a[i] != b[i]) {
                throw new RuntimeException("Broken!");
            }
        }
        System.out.println("OK");
    }
}

// $ java -Xint Bug
// OK

// $ java -Xcomp -XX:-TieredCompilation Bug
// Exception in thread "main" java.lang.RuntimeException: Broken!
// at Bug.main(Bug.java:15)

This may cause loss of data (although in few cases) so I would change the priority to P2.

Affect versions: 13, 14, 15, 16, 17 (both x86 and AArch64) and 11u (x86-only)