cmd/compile: eagerly CalcStructSize for synthetic ABI types

The next CL is going to replace Type.Width with Type.Size(), but
Type.Size() isn't safe to call concurrently. So this CL calls
CalcStructSize, which *is* allowed to be used concurrently, but then
it's the caller's responsibility to ensure it's called right after
NewStruct.

Change-Id: If9cd81650ccb3a867b4449af757375fa56227901
Reviewed-on: https://go-review.googlesource.com/c/go/+/345483
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/abi/abiutils.go

diff --git a/src/cmd/compile/internal/abi/abiutils.go b/src/cmd/compile/internal/abi/abiutils.go
index d657ddc..24f34b8 100644
--- a/src/cmd/compile/internal/abi/abiutils.go
+++ b/src/cmd/compile/internal/abi/abiutils.go
@@ -722,14 +722,17 @@
 			types.NewField(nxp, fname("len"), ui),
 			types.NewField(nxp, fname("cap"), ui),
 		})
+		types.CalcStructSize(synthSlice)
 		synthString = types.NewStruct(types.NoPkg, []*types.Field{
 			types.NewField(nxp, fname("data"), unsp),
 			types.NewField(nxp, fname("len"), ui),
 		})
+		types.CalcStructSize(synthString)
 		synthIface = types.NewStruct(types.NoPkg, []*types.Field{
 			types.NewField(nxp, fname("f1"), unsp),
 			types.NewField(nxp, fname("f2"), unsp),
 		})
+		types.CalcStructSize(synthIface)
 	})
 }