cmd/gc: use escape analysis result for make([]T, constant
cmd/gc: use escape analysis result for make([]T, constant

Escape analysis already gives that the underlying array
does not escape but the result was ignored.

Fixes issue 5484.

R=golang-dev, dave, daniel.morsing
CC=golang-dev
https://codereview.appspot.com/9662046

apparentlymart/golang,gnanderson/go,apparentlymart/golang,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,gnanderson/go,gnanderson/go,pombredanne/go-deleteme,gnanderson/go,tv42/old-go,pombredanne/go-deleteme,gnanderson/go,pombredanne/go-deleteme,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,tv42/old-go,gnanderson/go,apparentlymart/golang,gnanderson/go,tv42/old-go