XPG5 support for strptime introduces pivoting year support so
    that years in the range 0 to 68 are in the 21st century, and
    years in the range 69-99 are in the 20th century.

    With DECC$XPG4_STRPTIME enabled, XPG5 support for the pivoting
    year is disabled and all years in the range 0 to 99 are in the
    current century.