Revert of cmd/compile: ignore contentEscapes for marking nodes as escaping

Reason for revert: broke the build due to cherrypick;
relies on an unsubmitted parent CL.

Original issue's description:
> cmd/compile: ignore contentEscapes for marking nodes as escaping
> 
> We can still stack allocate and VarKill nodes which don't
> escape but their content does.
> 
> Fixes #16996
> 
> Change-Id: If8aa0fcf2c327b4cb880a3d5af8d213289e6f6bf
> Reviewed-on: https://go-review.googlesource.com/28575
> Run-TryBot: Keith Randall <khr@golang.org>
> TryBot-Result: Gobot Gobot <gobot@golang.org>
> Reviewed-by: David Chase <drchase@google.com>
> 

Change-Id: Ie1a325209de14d70af6acb2d78269b7a0450da7a
Reviewed-on: https://go-review.googlesource.com/28578Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/esc.go

@@ -1572,7 +1572,7 @@ func esccall(e *EscState, n *Node, up *Node) {
 		}
 
 		if haspointers(t.Type) {
-			if escassignfromtag(e, note, nE.Escretval, src)&EscMask == EscNone && up.Op != ODEFER && up.Op != OPROC {
+			if escassignfromtag(e, note, nE.Escretval, src) == EscNone && up.Op != ODEFER && up.Op != OPROC {
 				a := src
 				for a.Op == OCONVNOP {
 					a = a.Left

test/live.go

@@ -643,13 +643,3 @@ func good40() {
 	printnl() // ERROR "live at call to printnl: autotmp_[0-9]+ ret$"
 	_ = t
 }
-
-func ddd1(x, y *int) { // ERROR "live at entry to ddd1: x y$"
-	ddd2(x, y) // ERROR "live at call to ddd2: autotmp_[0-9]+$"
-	printnl()  // nothing live here.  See issue 16996.
-}
-func ddd2(a ...*int) { // ERROR "live at entry to ddd2: a$"
-	sink = a[0]
-}
-
-var sink *int

test/live_ssa.go

@@ -646,11 +646,3 @@ func good40() {
 	printnl() // ERROR "live at call to printnl: autotmp_[0-9]+ ret$"
 	_ = t
 }
-
-func ddd1(x, y *int) { // ERROR "live at entry to ddd1: x y$"
-	ddd2(x, y) // ERROR "live at call to ddd2: autotmp_[0-9]+$"
-	printnl()  // nothing live here.  See issue 16996.
-}
-func ddd2(a ...*int) { // ERROR "live at entry to ddd2: a$"
-	sink = a[0]
-}