libdw: Don't free uninitialized Dwarf_Abbrev_Hash's of "fake" CUs.

libdw: Don't free uninitialized Dwarf_Abbrev_Hash's of "fake" CUs.

fake_{loc,loclists,addr}_cu are Dwarf_CUs that are created separate from
all the others, so their contents are minimal and mostly initialized by
a calloc. On dwarf_end however, they are freed through the same code path
as all the others, so they call DAH_free like all the others. This changes
that so that these three are exempt from DAH and split-DWARF matters, and
swaps the calloc for a malloc so Memcheck will catch any others.

Signed-off-by: Jonathon Anderson <jma14@rice.edu>