Support 32 byte alignment of code on xarch (#2249)

Support 32 byte alignment of code on xarch (#2249)

* Support 32 byte alignment of code on xarch

Update jit and runtime to allow jit to ask for code to be 32 byte aligned.
Request 32 byte alignment for Tier1 methods on x86/x64.

Add minimal crossgen support; one can imagine requesting or choosing 32 byte
alignment for crossgenned code, but that is left as future work.

This should provide some measure of performance stability, in particular for
microbenchmarks or other code where performance depends crucially on a few
branches.

It may or may not improve performance. If/when there are regressions we can
contemplate updating the jit to add intra-method padding to address alignment
sensitive code layout (e.g. dotnet/coreclr#11607).

This will require a jit GUID update in addition to the changes here.

* restrict to larger methods with loops; don't update zapper

* new jit GUID

* fix target ifdef name