cmd/compile: use internal/buildcfg for checking newinliner enable
internal/goexperiment reports what GOEXPERIMENT the compiler itself was
compiled with, not what experiment to use for the object code that the
compiler is compiling.
Fixes #64189
Change-Id: I892d78611f8c76376032fd7459e755380afafac6
Reviewed-on: https://go-review.googlesource.com/c/go/+/542995
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com> Reviewed-by: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Than McIntosh <thanm@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>