doc: Install only "-posix" MinGW compiler when possible

Author: hebasto

doc/build-windows.md

@@ -48,8 +48,17 @@ Acquire the source in the usual way:
 ## Building for 64-bit Windows
 
 The first step is to install the mingw-w64 cross-compilation tool chain:
+  - on modern systems (Ubuntu 21.04 Hirsute Hippo or newer, Debian 11 Bullseye or newer):
 
-    sudo apt install g++-mingw-w64-x86-64
+```sh
+sudo apt install g++-mingw-w64-x86-64-posix
+```
+
+  - on older systems:
+
+```sh
+sudo apt install g++-mingw-w64-x86-64
+```
 
 Once the toolchain is installed the build steps are common: