Rework the test to work with any number of std packages. This was done
to include a few funcs from unicode/utf8. Adding more will be much
simpler too.

While at it, add more runtime funcs by searching for "inlined" or
"inlining" in the git log of its directory. These are: addb, subtractb,
fastrand and noescape.

Updates #21851.

Change-Id: I4fb2bd8aa6a5054218f9b36cb19d897ac533710e
Reviewed-on: https://go-review.googlesource.com/63611
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>