cmd/compile: use better fatal message for staticValue1

So the position of the wrong assignment statement will be reported,
instead of using incorrect base.Pos one.

Notice while fixing issue #73823.

Change-Id: I53f240bf99d11b5f5082ee4ca0903d9f099881b6
Reviewed-on: https://go-review.googlesource.com/c/go/+/675495
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Cuong Manh Le <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Mateusz Poliwczak <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: David Chase <[email protected]>

Author: cuonglm

src/cmd/compile/internal/ir/expr.go

@@ -912,12 +912,12 @@ FindRHS:
 				break FindRHS
 			}
 		}
-		base.Fatalf("%v missing from LHS of %v", n, defn)
+		base.FatalfAt(defn.Pos(), "%v missing from LHS of %v", n, defn)
 	default:
 		return nil
 	}
 	if rhs == nil {
-		base.Fatalf("RHS is nil: %v", defn)
+		base.FatalfAt(defn.Pos(), "RHS is nil: %v", defn)
 	}
 
 	if Reassigned(n) {

src/cmd/compile/internal/ir/reassignment.go

@@ -178,12 +178,12 @@ FindRHS:
 				break FindRHS
 			}
 		}
-		base.Fatalf("%v missing from LHS of %v", n, defn)
+		base.FatalfAt(defn.Pos(), "%v missing from LHS of %v", n, defn)
 	default:
 		return nil
 	}
 	if rhs == nil {
-		base.Fatalf("RHS is nil: %v", defn)
+		base.FatalfAt(defn.Pos(), "RHS is nil: %v", defn)
 	}
 
 	if _, ok := ro.singleDef[n]; !ok {