Makefile: Define $(LD)

For clarity, use $(LD) rather than $(CC) for linking.

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>
Makefile: Explicitly link against static library

When both the shared and static library are available, 'pstore'
and 'test-pstore' may link against either of them. Make the build
deterministic by explicitly linking against the static library.

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>
Merge branch 'fixes/linkage' of git://github.com/jvirtanen/pstore