Improve Irrlicht instructions (#14055)

Specify the version when cloning.
Move instructions from CMakeLists to docs/compiling/.

CMakeLists.txt

@@ -114,9 +114,7 @@ else()
 	find_package(IrrlichtMt QUIET)
 	if(NOT TARGET IrrlichtMt::IrrlichtMt)
 		string(CONCAT explanation_msg
-			"The Minetest team has forked Irrlicht to make their own customizations. "
-			"It can be found here: https://github.com/minetest/irrlicht\n"
-			"For example use: git clone --depth=1 https://github.com/minetest/irrlicht lib/irrlichtmt\n")
+			"You must install IrrlichMt as described in docs/compiling/\n")
 		if(BUILD_CLIENT)
 			message(FATAL_ERROR "IrrlichtMt is required to build the client, but it was not found.\n${explanation_msg}")
 		endif()

doc/compiling/linux.md

@@ -71,7 +71,7 @@ Download source (this is the URL to the latest of source repository, which might
 
 Download IrrlichtMt to `lib/irrlichtmt`, it will be used to satisfy the IrrlichtMt dependency that way:
 
-    git clone --depth 1 https://github.com/minetest/irrlicht.git lib/irrlichtmt
+    git clone --depth 1 --branch "$(cat misc/irrlichtmt_tag.txt)" https://github.com/minetest/irrlicht.git lib/irrlichtmt
 
 Download source, without using Git:
 

doc/compiling/macos.md

@@ -22,8 +22,8 @@ cd minetest
 
 Download Minetest's fork of Irrlicht:
 
-```
-git clone --depth 1 https://github.com/minetest/irrlicht.git lib/irrlichtmt
+```bash
+git clone --depth 1 --branch "$(cat misc/irrlichtmt_tag.txt)" https://github.com/minetest/irrlicht.git lib/irrlichtmt
 ```
 
 ## Build

doc/compiling/windows.md

@@ -17,7 +17,12 @@ After you successfully built vcpkg you can easily install the required libraries
 vcpkg install zlib zstd curl[winssl] openal-soft libvorbis libogg libjpeg-turbo sqlite3 freetype luajit gmp jsoncpp opengl-registry gettext --triplet x64-windows
 ```
 
-- **Don't forget about IrrlichtMt.** The easiest way is to clone it to `lib/irrlichtmt` as described in the Linux section.
+- **Don't forget about IrrlichtMt.** The easiest way is to clone it to `lib/irrlichtmt`:
+
+```bat
+for /F %i in (misc\irrlichtmt_tag.txt) do git clone --depth 1 --branch %i https://github.com/minetest/irrlicht.git lib\irrlichtmt
+```
+
 - `curl` is optional, but required to read the serverlist, `curl[winssl]` is required to use the content store.
 - `openal-soft`, `libvorbis` and `libogg` are optional, but required to use sound.
 - `luajit` is optional, it replaces the integrated Lua interpreter with a faster just-in-time interpreter.