This patch adjusts the memory instrumentation to account for scalable vector types in allocas. Note that we don't allow scalable vector globals, so we don't need to update that codepath.
A couple points.
First, this simply disables the optimization for scalable allocas. We can revisit this in the future, but it requires a bit of plumbing to get scalable object sizes through the visitor to be useful.
Second, I am simply disabling stack poisoning for scalable vector allocas. This is mostly for staging the change as I can't write a working test for memory instrumentation without doing so. I don't think it's unreasonable to do on it's own basis as without the bailout, we crash the compiler.
Differential Revision: https://reviews.llvm.org/D145259
