Deal with libtool 2.2 which doesn't let us use LT_ variables. (bug 15692)

Libtool-2.2 introduces new restrictions. So now it does not allow LT_*
variables as it includes marcros:

m4_pattern_forbid([^_?LT_[A-Z_]+$])

Rename the LT_ variables to LIBT_ to work around this restriction.
3 files changed