Hi Daniel,
I consider it a documentation request, please re-assign if needed.
user and group stay as is, but there are indeed many outdated points and a weird mix of Oracle/MariaDB.
Example of outdated points, just at the first glance:
MySQL 5.5 is the current development release series.
MySQL 5.1 is the current General Availability (Production)
Example of the weird mix:
Installing and Upgrading MariaDB
...
Normally, it is best
to use precompiled binary distributions of MySQL that are built
specifically for optimal performance on Windows by Oracle
Corporation.
Part of the issue here is that the INSTALL-SOURCE file we have is from MySQL 5.1.x with an introductory section that I added back when we were still on MariaDB 5.1.x. The INSTALL-SOURCE file in MySQL source tarballs is just a copy-paste of Chapter 2 of the MySQL manual. The introductory section is our only addition.
There are four things we can do here:
1. remove Chapter 2 of the MySQL manual from the file and just point people at the knowledgebase.
2. update the file so that it includes the MySQL 5.5.x INSTALL-SOURCE file.
3. Start from scratch and copy the relevant KB page(s) into the file.
4. Do #2 and then go through the file paragraph by paragraph and update it with MariaDB specific instructions.
#1 and #2 are both very easy to do. #1 is what we do for the INSTALL-WIN-SOURCE file. #3 would not be too difficult either since it's just copy-pasting from the KB. The only issue there is to make sure to keep it updated with every release so that it has the latest information (something we would avoid if we went with #1). #4 would be the most difficult and I don't know how useful it would be either since we would basically be creating new, duplicate install docs.
I like option #1 best. The KB is where we keep our docs, and we should strongly encourage people to go there. Including chapter 2 of the MySQL manual made sense when we were getting started, especially since that's what MySQL does, but it just causes confusion now.
Any thoughts? Other options? Questions?
I'm fine with #1, only maybe in addition to the KB link already existing in the file, it would make sense to add a more specific one (the one that is already there points at a high-level contents list "Getting, Installing, and Upgrading MariaDB").
This one looks closer: https://kb.askmonty.org/en/compiling-mariadb-from-source/
Yes, please go ahead!
As MariaDB is not including configure script anymore, installation must be made using cmake.
In https://kb.askmonty.org/en/compiling-mariadb-from-source/ I still find all references to configure, but some hint that newer versions use cmake (and just a link to http://www.cmake.org/)
I would be nice to find there that command to show all configuration options is:
$ cmake . -LH
and an example of how they should be entered, i.e.:
$ cmake . -DCMAKE_INSTALL_PREFIX:PATH=/usr/local/maria
Looking for that information hinders source installation
MySQL/Oracle information on this topic is quite extensive:
http://dev.mysql.com/doc/internals/en/cmake-howto-long-version.html
You can use MySQL/Oracle information, too 
It is actually too extensive. I think. It was not written by Oracle folks as end-user documentation, the initial purpose of this document was to introduce MySQL developers to the new tool, therefore it contains quite a lot of cmake basics, such as parameter discovery and CMAKE_INSTALL_PREFIX.
Before closing this task I'll edit the https://kb.askmonty.org/en/compiling-mariadb-from-source/ to improve it.
I've updated the following articles:
https://kb.askmonty.org/en/build-environment-setup-for-linux/
https://kb.askmonty.org/en/source-getting-the-mariadb-source-code/
https://kb.askmonty.org/en/generic-build-instructions/
Things are much improved documentation-wise, so closing.