Fix wrong format specification in display_selector()

Fix wrong format specification in display_selector()

There are a wrong format strings in function display_selector() in
file windows-nat.c. This leads to build error using Cygwin on Windows.
LDT_ENTRY.HighWord is a DWORD, which is unsigned long int, so the
format specification should be for long int, not simply int.

gdb/ChangeLog:
2019-03-17  Vladimir Martyanov  <vilgeforce@gmail.com>

    PR gdb/24351
    * windows-nat.c (display_selector): Format specifications fixed