MSYS2 doesn't have a "mingw-w64-gcc" package, and also needs "make".

docs/how-to/build-from-source.md

@@ -40,13 +40,15 @@ you'll need these packages:
 
 On Windows,
 you should install [MSYS2][],
-and from there install `mingw-w64-gcc`
+and from there install `make` and `mingw-w64-ucrt-x86_64-gcc`:
+
+    pacman -S make mingw-w64-ucrt-x86_64-gcc
+
+[MSYS2]: https://www.msys2.org/
 
 On macOS,
 installing the Xcode command-line tools should be enough.
 
-[MSYS2]: https://www.msys2.org/
-
 Building
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