Change DataExtractor's ReadInt* and ReadSwapInt* routines, as well as
GetU32 and GetU64, to use memcpy to copy bytes into a local buffer instead
of having a (uint64_t *) etc local variable, pointing to the address, and
dereferencing it.  If compiled on a CPU where data alignment is required
(e.g. the LDM instruction on armv7) and we try to GetU64 out of a mmap'ed
DWARF file, that 8 byte quantity may not be world aligned and the program
can get an unaligned memory access fault.

<rdar://problem/15849231>