unicode/norm: look for symbols in TestLinking
unicode/norm: look for symbols in TestLinking

Previously, we just inspected sizes to tell if the linker was stripping
unnecessary bits, so, actually look for symbols.

Fixes golang/go#34209

Change-Id: Iec355ac46a967aeca9c0c1a950ead6b563c5e84e
Reviewed-on: https://go-review.googlesource.com/c/text/+/221104
Run-TryBot: Jeremy Faller <b3f594e10a9edcf5413cf1190121d45078c62290@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Marcel van Lohuizen <a22d082192f3ccf984644a4f482781f4c2d65180@golang.org>

golang/text