cmd/compile: add more runtime funcs to inline test

This is based from a list that Keith Randall provided in mid-2016. These
are all funcs that, at the time, were important and small enough that
they should be clearly inlined.

The runtime has changed a bit since then. Ctz16 and Ctz8 were removed,
so don't add them. stringtoslicebytetmp was moved to the backend, so
it's no longer a Go function. And itabhash was moved to itabHashFunc.

The only other outlier is adjustctxt, which is not inlineable at the
moment. I've added a TODO and will address it myself in a separate
commit.

While at it, error if any funcs in the input table are duplicated.
They're never useful and typos could lead to unintentionally thinking a
function is inlineable when it actually isn't.

And, since the lists are getting long, start sorting alphabetically.

Finally, rotl_31 is only defined on 64-bit architectures, and the added
runtime/internal/sys funcs are assembly on 386 and thus non-inlineable
in that case.

Updates #21851.

Change-Id: Ib99ab53d777860270e8fd4aefc41adb448f13662
Reviewed-on: https://go-review.googlesource.com/65351


Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@golang.org>