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+Default generator
+-----------------
+
+As of CMake 3.18, the default generator (unless set explicitly) is:
+  * the newest Visual Studio or "NMake Makefiles" on Windows,
+  * "Unix Makefiles" otherwise.
+This is regardless of whether any executables like gcc, cl or make are
+available [1].
+
+Makefile generators
+-------------------
+
+CMake has a number of "... Makefiles" generators.  "Unix Makefiles" uses
+gmake/make/smake, whichever is found first, and cc/c++ for compiler
+detection [2].  "MinGW Makefiles" looks for mingw32-make.exe in a number of
+well-known locations, uses gcc/g++ directly, and is aware of windres [3].  In
+addition, "Unix Makefiles" uses /bin/sh as the SHELL value in the Makefile,
+while the MinGW version uses cmd.exe.  I don't think it matters on Windows
+though, since the non-existent /bin/sh is ignored anyway [4].  "NMake
+Makefiles" is similar, except it defaults to using cl [5].
+
+It's important to _not_ use the -A parameter with any of the Makefile
+generators - it's an error.  This goes for "NMake Makefiles" also.  "NMake
+Makefiles" doesn't attempt to search for installed Visual Studio compilers,
+you need to use it from one of the Visual Studio-provided shells.
+
+Visual Studio generators
+------------------------
+
+These are special.  They ignore the CMAKE_<LANG>_COMPILER parameters and use
+cl by default [9].  They support specifying the toolset to use via the -T
+parameter (the "Platform Toolset" value in the project's properties) since
+3.18 [10].  The toolset list varies between Visual Studio versions, and I'm
+too lazy to learn exactly which version supports which toolsets.
+
+cmake --build uses msbuild with Visual Studio generators.  You can pass the
+path to a different cl.exe by doing something like
+
+    msbuild ... /p:CLToolExe=another-cl.exe /p:CLToolPath=C:\parent\dir
+
+It's important that the generators for Visual Studio 2017 or older use Win32
+Win32 as the default platform [12].  Because of that, we need to pass the -A
+parameter.
+
+mingw32-make vs make
+--------------------
+
+No idea what the actual differences are.  The explanation in the FAQ [6]
+about how GNU make "is lacking in some functionality and has modified
+functionality due to the lack of POSIX on Win32" isn't terribly helpful.
+
+It's important that you can install either on Windows (`choco install make`
+for GNU make and `choco install mingw` to install a MinGW-w64 distribution
+with mingw32-make.exe included).  Personally, I don't see any difference
+between using either make.exe or mingw32-make.exe w/ CMake on Windows.  But,
+since MinGW-w64 distributions do include mingw32-make.exe and not make.exe,
+we'll try to detect that.
+
+Cross-compilation
+-----------------
+
+If you want to e.g. build x86 binary on x64 and vice versa, the easiest way
+seems to be to make a CMake "toolchain file", which initializes the proper
+compiler flags (like -m64/-m32, etc.).  Such file could look like this:
+
+    set(CMAKE_C_COMPILER   gcc)
+    set(CMAKE_C_FLAGS      -m32)
+    set(CMAKE_CXX_COMPILER g++)
+    set(CMAKE_CXX_FLAGS    -m32)
+
+You can then pass the path to it using the CMAKE_TOOLCHAIN_FILE parameter.
+
+If you use the Visual Studio generators, just use the -A parameter, like "-A
+Win32".
+
+As a side note, if you want to cross-compile between x86 and x64 using GCC on
+Ubuntu, you need to install the gcc-multilib package.
+
+Windows & Clang
+---------------
+
+Using Clang on Windows is no easy task, of course.  Prior to 3.15, there was
+no support for building things using the clang++.exe executable, only
+clang-cl.exe was supported [7].  If you specified -DCMAKE_CXX_COMPILER=clang++,
+CMake would stil pass MSVC-style command line options to the compiler (like
+/MD, /nologo, etc.), which clang++ doesn't like [8].
+
+So, in summary, you can only use clang++ since 3.15.  clang-cl doesn't work
+with Visual Studio generators unless you specify the proper toolset using the
+-T parameter.  You can set the ClToolExe property using msbuild, but while
+that might work in practice, clang-cl.exe needs to map some unsupported
+options for everything to work properly.  For an example of how this is done,
+see the LLVM.Cpp.Common.* files at [11].
+
+I recommend using Clang (either clang-cl or clang++ since 3.15) using the
+"NMake Makefiles" generator.
+
+References
+----------
+
+[1]: cmake::EvaluateDefaultGlobalGenerator
+     https://github.com/Kitware/CMake/blob/v3.18.4/Source/cmake.cxx
+[2]: https://github.com/Kitware/CMake/blob/v3.18.4/Source/cmGlobalUnixMakefileGenerator3.cxx
+[3]: https://github.com/Kitware/CMake/blob/v3.18.4/Source/cmGlobalMinGWMakefileGenerator.cxx
+[4]: https://www.gnu.org/software/make/manual/html_node/Choosing-the-Shell.html
+[5]: https://github.com/Kitware/CMake/blob/v3.18.4/Source/cmGlobalNMakeMakefileGenerator.cxx
+[6]: http://mingw.org/wiki/FAQ
+[7]: https://cmake.org/cmake/help/v3.15/release/3.15.html#compilers
+[8]: https://github.com/Kitware/CMake/blob/v3.14.7/Modules/Platform/Windows-Clang.cmake
+[9]: https://gitlab.kitware.com/cmake/cmake/-/issues/19174
+[10]: https://cmake.org/cmake/help/v3.8/release/3.8.html
+[11]: https://github.com/llvm/llvm-project/tree/e408935bb5339e20035d84307c666fbdd15e99e0/llvm/tools/msbuild
+[12]: https://cmake.org/cmake/help/v3.18/generator/Visual%20Studio%2015%202017.html