build: corrected --libs flags

build: corrected --libs flags

Stuff to keep in mind:
- LDFLAGS are reserved for linker *flags*;
- LIBADD is a per-library variable and must include object/libraries to
  link library against;
- LDADD is the per-program version of LIBADD;
- external objects/libraries should be specified with -L and -l;
- internal objects/libraries should be specified directly (adding full
  path to .la for shared internal libraries);
- objects/libraries order is significative: any item can depend on the
  following items but not on the preceeding ones.