Assume local variables are naturally aligned.

Assume local variables are naturally aligned.

Using alignment = 0 to signify natural alignment will allow to discern
between loads/stores for stack variables, and dereferencing generic
pointers.

Bug swiftshader:78

Change-Id: I6d9c1728fb9858ca57380bc6bfafc7fb2fa5feae
Reviewed-on: https://swiftshader-review.googlesource.com/10968
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>