Switch to memcpy for accessing misaligned data.

Bug: http://b/31532493

Using misaligned pointers forces us to potentially take the address of
members in a packed structure (which is now a warning/error in the
latest Clang). Using memcpy() is the proper way to handle this kind of
problem, as the compiler can insert the proper instructions (and usually
elide the memcpy() entirely).

Test: Built correctly with updated compilers.
Change-Id: Ia1f6eb62cf19404ff76b71d3c6c7ffffa1403120