cmd/gc: enable inlining in generated method wrappers.
Method calls on interfaces with large stored values
will call the pointer receiver method which may be
a wrapper over a method with value receiver.
This is particularly inefficient for very small bodies.
Inlining the wrapped method body saves a potentially expensive
function call.
benchmark old ns/op new ns/op delta
BenchmarkSortString1K 802295 641387 -20.06%
BenchmarkSortInt1K 359914 238234 -33.81%
BenchmarkSortInt64K
35764226 22803078 -36.24%
Fixes #4707.
R=golang-dev, daniel.morsing, rsc
CC=golang-dev
https://golang.org/cl/
7214044