Automake explicitly recognizes the use of $(LIBOBJS) and
$(ALLOCA), and uses this information, plus the list of
LIBOBJS files derived from configure.in to automatically
include the appropriate source files in the distribution (see Dist).
These source files are also automatically handled in the
dependency-tracking scheme; see See Dependencies.
$(LIBOBJS) and $(ALLOCA) are specially recognized in any
_LDADD or _LIBADD variable.