make sure that stdio file buffer get allocated.
* winsup.api/ltp/stat06.c (high_address_setup): On cygwin, area
after sbrk(0) may be available, use 0xffff0000 as "high address".
* winsup.api/ltp/symlink01.c: Perform all tests. Mark those tests that
don't work on cygwin with '-1'. Close open files so that temporary
directory can be deleted on exit.
* winsup.api/ltp/vfork01.c: New test.
variable CYGWIN_TESTSUITE_TESTS is set. Use its value as regular
expression to filter test names.
* winsup.api/ltp/symlink01.c (creat_path_max): Provide explicit
buffer to getcwd to conform to standards and avoid memory leak.
(do_chdir): Ditto.
