runtime: remove trailing empty arrays in structs

The ones at the end of M and G are just used to compute
their size for use in assembly.  Generate the size explicitly.
The one at the end of itab is variable-sized, and at least one.
The ones at the end of interfacetype and uncommontype are not
needed, as the preceding slice references them (the slice was
originally added for use by reflect?).
The one at the end of stackmap is already accessed correctly,
and the runtime never allocates one.

Update #9401

Change-Id: Ia75e3aaee38425f038c506868a17105bd64c712f
Reviewed-on: https://go-review.googlesource.com/2420
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/runtime/runtime2.go

@@ -215,7 +215,6 @@ type g struct {
 	gopc         uintptr // pc of go statement that created this goroutine
 	racectx      uintptr
 	waiting      *sudog // sudog structures this g is waiting on (that have a valid elem ptr)
-	end          [0]byte
 }
 
 type mts struct {
@@ -298,7 +297,6 @@ type m struct {
 	notesig *int8
 	errstr  *byte
 	//#endif
-	end [0]byte
 }
 
 type p struct {
@@ -425,7 +423,7 @@ type itab struct {
 	link   *itab
 	bad    int32
 	unused int32
-	fun    [0]uintptr
+	fun    [1]uintptr // variable sized
 }
 
 // Lock-free stack node.