[dev.ssa] Merge remote-tracking branch 'origin/master' into mergebranch

Semi-regular merge from tip to dev.ssa.

Two fixes:
1) Mark selectgo as not returning.  This caused problems
   because there are no VARKILL ops on the selectgo path,
   causing things to be marked live that shouldn't be.
2) Tell the amd64 assembler that addressing modes like
   name(SP)(AX*4) are ok.

Change-Id: I9ca81c76391b1a65cc47edc8610c70ff1a621913

src/cmd/internal/obj/link.go

@@ -604,12 +604,13 @@ type Link struct {
 	Autosize           int32
 	Armsize            int32
 	Pc                 int64
-	Diag               func(string, ...interface{})
+	DiagFunc           func(string, ...interface{})
 	Mode               int
 	Cursym             *LSym
 	Version            int
 	Textp              *LSym
 	Etextp             *LSym
+	Errors             int
 
 	// state for writing objects
 	Text  *LSym
@@ -618,6 +619,11 @@ type Link struct {
 	Edata *LSym
 }
 
+func (ctxt *Link) Diag(format string, args ...interface{}) {
+	ctxt.Errors++
+	ctxt.DiagFunc(format, args...)
+}
+
 // The smallest possible offset from the hardware stack pointer to a local
 // variable on the stack. Architectures that use a link register save its value
 // on the stack in the function prologue and so always have a pointer between