Unaligned accesses are undefined behavior, but they're common in our
ELF binary patching code for variable length instruction sets (namely
x86).

We can use memcpy() and rely on target-specific compiler optimizations
to make it efficient. Utility functions and classes were added to aid
readability.

Bug b/119823623

Change-Id: I8a82672a0d18d1e1783f580eb629f8cc09a009cd
Reviewed-on: https://swiftshader-review.googlesource.com/c/22828Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>