build: don't try to guess the include directory

Signed-off-by: Evan Nemerson <evan@coeus-group.com>
build: add archive library install directory for mingw

Signed-off-by: Evan Nemerson <evan@coeus-group.com>
build: fix LZO library detection

Signed-off-by: Evan Nemerson <evan@coeus-group.com>
Drop libltdl dependency.

Fixes https://github.com/quixdb/squash/issues/38
Fixes https://github.com/quixdb/squash/issues/62

Signed-off-by: Evan Nemerson <evan@coeus-group.com>