cmInstallExportGenerator: expose the temporary directory

This needs to be known so that C++ module properties for the install can
be staged beside the other files.

Always perform the MD5 transformation (in non-bootstrap builds) so that
the path can be computed prior to generation (where it used the longest
configuration name to detect too-long paths). Update tests to expect the
always-present MD5 value. Note that this improves robustness of the test
suite as testing in a too-long path may have triggered the MD5
conversion anyways.
5 files changed