go/types: StdSizes needs to know about new complex64 alignment

[mdempsky]

golang.org/cl/19800 changed complex64's alignment on 64-bit platforms from 8 to 4. I originally didn't think go/types.StdSizes needed to care about this because of past discussion about StdSizes vs cmd/compile on #12886, but @josharian pointed out cmd/vet relies on StdSizes for validating x+NN(FP) assembly addresses.

/cc @griesemer

[griesemer]

We should probably provide a GCSizes (better name welcome) that matches cmd/compile exactly and that's the one all clients use that depend on the same size computations as cmd/compile.

[gopherbot]

CL https://golang.org/cl/31939 mentions this issue.

[josharian]

We should probably provide a GCSizes

SGTM. Filed #17586 for that. Thanks, @mdempsky, for fixing this in the meantime.

[RLH]

GC means garbage collector. gc means go compiler. It is unfortunate but it is what it is. We really need another name for this.