Fix some .debug checking and gnu hash xlate logic

[Mark Wielaard]

Hi,

The last fuzzer found some use (checking) of undefine/uninitialized
data. Either of these two patches will fix that:

 [PATCH 1/2] libelf: memmove any extra bytes left by elf_cvt_gnuhash
 [PATCH 2/2] libdw: Use elf_rawdata when checking .debug section

Note that the bad data wouldn't actually be used, just checked for
validity. But these patches make sure the result is deterministic.

Cheers,

Mark