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

This reverts commit 649eba4229cc0a22bdd8160cf4d19470aae9300c.

The bug had a different cause and was fixed in
7f2a2d2b05e64ee425f95d189ed6ef32d8895ab9.

Change-Id: I0f2ca7dca59a13843acdea1d35671f841b071d7b
Reviewed-on: https://gerrit.libreoffice.org/7852
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>