Try to read the libdivecomputer.la file (created by GNU libtool)

Getting dependency information for static libraries requires extra
files. Libtool creates .la files, which are "industry standard". qmake
has its own .prl files, but it can create .la in a pinch if necessary.

This change allows us to get the actual dependency information from
libdivecomputer, without having to guess whether it linked to something
else or not. If it changes in the future, we shouldn't have to do
anything.

Signed-off-by: Thiago Macieira <thiago@macieira.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>