Fix cross-linking issues

When using AC_CHECK_LIB, the LIBS variable is expanded to include
the libraries, and consequently all built targets are linked against
these libraries.

This commit fixes the cross linking by ensuring each part of the
library and binaries are only linked to exactly what they need,
i.e. no gdbm linking on bt-daemon and buxtonctl.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>