Revert "cmd/compile: allow more args in StructMake folding rule"

This reverts commit 72e8237 (CL 693615)

Reason for revert: still causing compiler failures on Google test code

Change-Id: I4a7850c321d95ed7803d56866bb0c524c7a377d3
Reviewed-on: https://go-review.googlesource.com/c/go/+/695015
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

Author: randall77

src/cmd/compile/internal/ssa/_gen/generic.rules

@@ -921,7 +921,7 @@
   @x.Block (Load <v.Type> (OffPtr <v.Type.PtrTo()> [t.FieldOff(int(i))] ptr) mem)
 
 // Putting struct{*byte} and similar into direct interfaces.
-(IMake _typ (StructMake ___)) => imakeOfStructMake(v)
+(IMake _typ (StructMake val)) => imakeOfStructMake(v)
 (StructSelect [_] (IData x)) => (IData x)
 
 // un-SSAable values use mem->mem copies