Disable LTO for now - suspected cause of fdo#73464.

Change-Id: I8c9ff1342ecb6b7a990ea643c505e9dedf5de659
Reviewed-on: https://gerrit.libreoffice.org/7681
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>