Tests: Skip RunCMake.file INSTALL-FOLLOW_SYMLINK_CHAIN case on Cygwin

This case was added by commit e3ff7ced63 (file(INSTALL): Add
FOLLOW_SYMLINK_CHAIN argument, 2019-05-16, v3.15.0-rc1~103^2).
Skip it on Cygwin because it fails due to `foo/../` pairs being
flattened away in symlinks.
2 files changed