cmd/compile: don’t consider recursive calls for inlining

cmd/compile: don’t consider recursive calls for inlining

We will never inline recursive calls.
Rather than simulate the recursion until we hit
the complexity ceiling, just bail early.

Also, remove a pointless n.Op check.
visitBottomUp guarantees that n will be an
ODCLFUNC, and caninl double-checks it.

Change-Id: Ifa48331686b24289d34e68cf5bef385f464b6b92
Reviewed-on: https://go-review.googlesource.com/27462
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>