Support LLD ThinLTO cache/threshold option

LLD has different option syntax for specifying ThinLTO cache. Change it
to LLD syntax and drop the support for GOLD, since there aren't many
projects that are linked with it.

Test: USE_THINLTO_CACHE=true m
Change-Id: I5c6c5281a05793414a6387d52ae48d9b43822ee9