Most basic test of inlining by reduction.

-- go.mod --
module testdata
go 1.12

-- a/a.go --
package a

var _ = zero() //@ inline(re"zero", zero)

func zero() int { return 0 }

-- zero --
package a

var _ = (0) //@ inline(re"zero", zero)

func zero() int { return 0 }
