This should take care of the define for leveldb:

diff --git a/configure.ac b/configure.ac
index f7de4c9..2690477 100644
--- a/configure.ac
+++ b/configure.ac
@@ -449,6 +449,8 @@ case $host in
    *openbsd*)
      LEVELDB_TARGET_FLAGS="-DOS_OPENBSD"
      ;;
+    *netbsd*)
+     LEVELDB_TARGET_FLAGS="-DOS_NETBSD"
    *)
      OTHER_OS=`echo ${host_os} | awk '{print toupper($0)}'`
      AC_MSG_WARN([Guessing LevelDB OS as OS_${OTHER_OS}, please check whether this is correct, if not add an entry to configure.ac.])

I'm confused about /usr/pkg, though. Is the system compiler not configured to check there by default?

NetBSD/pkgsrc developer here. If you simply allow standard CPPFLAGS and LDFLAGS in ./configure, then when this is built by pkgsrc to be linked against the library packages it depends on, pkgsrc will furnish the necessary -I and -L and -R flags for /usr/pkg, or for wherever pkgsrc is built to install into.

The system compiler intentionally doesn't automatically add /usr/pkg to the paths because /usr/pkg is the domain of packages, not of the compiler; pkgsrc can be built for any other location, e.g. /usr/pkg-20xxQy for a quarterly release or /home/alice/pkg for unprivileged installations; and what's in it may change as you install or remove packages, but pkgsrc has no record of things outside /usr/pkg that might be broken by that.

The best way to link against libraries installed in /usr/pkg or elsewhere by pkgsrc is just to package up bitcoin in pkgsrc (currently there's an old version in pkgsrc-wip -- patches welcome!); otherwise, software built outside pkgsrc is expected to pass the necessary -I/-L/-R flags as if for any custom library installation prefix.

@randolf What's required to move this forward?

At a minimum, please update 0dccc26 with a better commit title, rather than the GitHub default.
i.e "[build] Add db4_cxx to bitcoin_find_bdb48.m4".

Please also squash d3e58d2 through 30062f8 into a single commit. "[doc] Create build-netbsd.md" etc.

@fanquake Thanks; I'm new to GitHub.com and so I appreciate any assistance from you and anyone else. I did originally name this because I prefer this over default names, and at present I'm trying to figure out how to make changes to this Pull Request. I would love to move this forward, but I think I'm just stuck with a GitHub learning curve at present, so I certainly welcome all pointers and suggestions.

(None of the instructions for Squashing that I've tried seem to work because the various options instructed simply don't appear for me anywhere on the GitHub web site or within the GitHub Desktop software. If there are some reliable instructions to follow to Squash this, I'll gladly try it.)

It is not possible to squash on GitHub web. I am not familiar with GitHub desktop, but there are some notes in https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md#squashing-commits

@MarcoFalke I can "clone" on Unix but "checkout" always fails to find the .git file. "Allow edits from maintainers" is enabled, in case that's helpful.

I want to get Squash working (I'm assuming that I must be missing something), but if there's a time-constraint then I also don't want to cause any delays for the Bitcoin project overall.

No, there is no pressure and squashing makes the review easier, I presume.

I can "clone" on Unix but "checkout" always fails to find the .git file.

It probably said something like "cloning into bitcoin", so you'd first cd ./bitcoin/ and then git log -1 etc.

Thanks @MarcoFalke. I couldn't find the "Squash" feature 14 days ago (see my first comment on this Pull Request where I indicated that I'd like to do this), and I'm not finding it now. I looked into this for a while but didn't make any progress. If there's a guide you (or anyone) can point me to that will help me to get this Pull Request "squashed," I'd be happy to give it a try.

If there's a guide you (or anyone) can point me to that will help me to get this Pull Request "squashed," I'd be happy to give it a try.

I don't know of a guide offhand, but if you google git rebase squash you can find some tutorials. Basic idea is to run a command like git rebase -i $(git merge-base HEAD origin/master) which will open up your text editor and let you change the branch history. If you change the history from "pick pick pick..." to "pick squash squash..." this will combine separate commits into one commit.

@randolf I wrote these instructions for how to rebase and squash for a different cryptocurrency which might be of help https://gist.github.com/jcvernaleo/aa3f6c216f3df1f9c6b62d7f59a2a469#rebasing-one-of-your-existing-pull-requests

Thank you @ryanofsky -- I will look into that.

@jcvernaleo Okay, your instructions seem to be helpful, and I think I've made some progress on this now despite the fun with using "vi" to change "noop" to "s" (hopefully I can configure git to use a different editor, but I'll leave this for later). I was also prompted by the "git push" command for username and password, and then it all finished with "Everything is up-to-date."

I don't see any indication of changes on the GitHub.com web site though, but perhaps my upload is queued somewhere and I just have to wait? I'll check back later.

Thanks for your help!

noop will appear when you run git rebase --interactive HEAD

You should replace HEAD with HEAD~6 or 0dccc26~

@randolf git uses whatever default editor you have set as $EDITOR (or vi if that isn't set). So you can either set $EDITOR in your shell or set it just for gti like:

git config --global core.editor emacs

or whatever editor you prefer.

@jcvernaleo That worked very well, thank you.

@MarcoFalke So I saw 6 items in the list, each with "pick" as the first word. The "git push" command (which I had to login for, as expected), then reported the following:

* [new branch] HEAD -> bitcoin

On the GitHub.com web site, the "Compare" function still shows 6 changes, so if it's not Squashed yet I'm probably looking in the wrong place. There's so much to learn about using git (it seems to be a pretty extensive system), and I appreciate all the help from you and everyone else thus far.

@randolf you need to mark the commits as squash in the editor, see http://push.cwcon.org/learn/squashing-commits.html

@randolf Thanks for your work so far. I've created a new PR, squashing and updating the commit messages of your commits. All of your changes are still attributed to you. I'll close this PR, any further review can happen in #12294.

@fanquake Thanks for taking care of the Squashing for me. I'm still new to GitHub and so this is helpful to get things moving along. I appreciate it.