scripts/setlocalversion: also consider annotated tags of the form vx.y.z-${file_localversion}

Commit 6ab7e1f9

 ("setlocalversion: use only the correct release
tag for git-describe") was absolutely correct to limit which annotated
tags would be used to compute the -01234-gabcdef suffix. Otherwise, if
some random annotated tag exists closer to HEAD than the vX.Y.Z one,
the commit count would be too low.

However, since the version string always includes the
${file_localversion} part, now the problem is that the count can be
too high. For example, building an 6.4.6-rt8 kernel with a few patches
on top, I currently get

$ make -s kernelrelease
6.4.6-rt8-00128-gd78b7f406397

But those 128 commits include the 100 commits that are in
v6.4.6..v6.4.6-rt8, so this is somewhat misleading.

Amend the logic so that, in addition to the linux-next consideration,
the script also looks for a tag corresponding to the 6.4.6-rt8 part of
what will become the `uname -r` string. With this patch (so 29 patches
on top of v6.4.6-rt8), one instead gets

$ make -s kernelrelease
6.4.6-rt8-00029-gd533209291a2

While there, note that the line

  git describe --exact-match --match=$tag $tag 2>/dev/null

obviously asks if $tag is an annotated tag, but it does not actually
tell if the commit pointed to has any relation to HEAD. So remove both
uses of --exact-match, and instead just ask if the description
generated is identical to the tag we provided. Since we then already
have the result of

  git describe --match=$tag

we also end up reducing the number of times we invoke "git describe".

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>