Download the Eclipse installer (at writing the latest version is Neon.3) from https://www.eclipse.org/downloads/.
To run Eclipse you will need Java installed.
Download MinGW-W64 from https://sourceforge.net/projects/mingw-w64/.
Start up the Eclipse installer and update it if necessary. Once that’s done, select Eclipse IDE for C/C++ developers.
Go ahead and install it, but don’t launch it.
Open the MinGW-W64 installer and choose x86_64 architecture. Make sure the build revision is the highest possible and then continue.
Add the bin subfolder of where you installed MinGW to your Path variable. For me, this was C:\Program Files\mingw-w64\x86_64-7.1.0-posix-seh-rt_v5-rev0\mingw64\bin\.
Reboot if necessary, and then you’re done.