cmd/compile: no stmt flag set for two lines of code that do generate instructions

[aarzilli]

$ go version
go version go1.17 linux/amd64

it also reproduces on 1.17 windows/amd64 and 1.16.

Reproduction steps:

1. Compile the tests of package github.com/dolthub/dolt/go/libraries/doltcore/sqle with -gcflags='all=-N -l' (commit d2c3c987593fe82e0571ffd3fda09afd340b4634 will do this)
2. See the pcln table generated for github.com/dolthub/dolt/go/libraries/doltcore/sqle.NewTestEngine
3. Lines 120 and 121 have instructions generated but none of them have the stmt flag set

Originally reported as go-delve/delve#2664
cc @dr2chase

[dr2chase]

It happens in expand calls, not sure of the exact failure yet, other than the statement was hanging off an OpDereference.
To see for yourself:

git clone https://github.com/dolthub/dolt
cd dolt/go/libraries/doltcore/sqle
GOSSADIR=`pwd` GOSSAFUNC=NewTestEngine go test -c -gcflags=all='-N -l' .

[gopherbot]

Change https://golang.org/cl/344769 mentions this issue: cmd/compile: preserve statements better in expandCalls