The cfi bot is throwing an error because an object is being assigned
with memory containing an invalid vtable. This is caused by assigning
a chunk of memory to an object before calling placement new using that
memory.

This cl assigns the pointer after the object has been constructed to
avoid triggering this error.

Bug: chromium:1116053
Change-Id: I541d7dc0e884aed7470b97d7d1d91a9bb67edb2d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/47788Tested-by: Alexis Hétu <sugoi@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>