Formally drop support for building with upstream Irrlicht

It stopped working with (at least) the last commit.

.github/workflows/build.yml

@@ -132,7 +132,7 @@ jobs:
       - name: Install deps
         run: |
           source ./util/ci/common.sh
-          install_linux_deps --old-irr clang-9
+          install_linux_deps clang-9
 
       - name: Build prometheus-cpp
         run: |

CMakeLists.txt

@@ -78,7 +78,6 @@ if(NOT "${IRRLICHTMT_BUILD_DIR}" STREQUAL "")
 		# IrrlichtMtConfig.cmake
 		message(FATAL_ERROR "Could not find IrrlichtMtConfig.cmake in ${IRRLICHTMT_BUILD_DIR}/cmake.")
 	endif()
-# This is done here so that relative search paths are more reasonable
 elseif(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/lib/irrlichtmt")
 	message(STATUS "Using user-provided IrrlichtMt at subdirectory 'lib/irrlichtmt'")
 	if(BUILD_CLIENT)
@@ -108,9 +107,9 @@ else()
 
 		include(MinetestFindIrrlichtHeaders)
 		if(NOT IRRLICHT_INCLUDE_DIR)
-			message(FATAL_ERROR "Irrlicht or IrrlichtMt headers are required to build the server, but none found.\n${explanation_msg}")
+			message(FATAL_ERROR "IrrlichtMt headers are required to build the server, but none found.\n${explanation_msg}")
 		endif()
-		message(STATUS "Found Irrlicht headers: ${IRRLICHT_INCLUDE_DIR}")
+		message(STATUS "Found IrrlichtMt headers: ${IRRLICHT_INCLUDE_DIR}")
 		add_library(IrrlichtMt::IrrlichtMt INTERFACE IMPORTED)
 		# Note that we can't use target_include_directories() since that doesn't work for IMPORTED targets before CMake 3.11
 		set_target_properties(IrrlichtMt::IrrlichtMt PROPERTIES

README.md

@@ -223,8 +223,8 @@ Run it:
 - You can disable the client build by specifying `-DBUILD_CLIENT=FALSE`.
 - You can select between Release and Debug build by `-DCMAKE_BUILD_TYPE=<Debug or Release>`.
   - Debug build is slower, but gives much more useful output in a debugger.
-- If you build a bare server you don't need to have the Irrlicht or IrrlichtMt library installed.
-  - In that case use `-DIRRLICHT_INCLUDE_DIR=/some/where/irrlicht/include`.
+- If you build a bare server you don't need to compile IrrlichtMt, just the headers suffice.
+  - In that case use `-DIRRLICHT_INCLUDE_DIR=/some/where/irrlichtmt/include`.
 
 - Minetest will use the IrrlichtMt package that is found first, given by the following order:
   1. Specified `IRRLICHTMT_BUILD_DIR` CMake variable

cmake/Modules/MinetestFindIrrlichtHeaders.cmake

@@ -1,21 +1,13 @@
-# Locate Irrlicht or IrrlichtMt headers on system.
+# Locate IrrlichtMt headers on system.
 
-foreach(libname IN ITEMS IrrlichtMt Irrlicht)
-	string(TOLOWER "${libname}" libname2)
-
-	find_path(IRRLICHT_INCLUDE_DIR NAMES irrlicht.h
-		DOC "Path to the directory with IrrlichtMt includes"
-		PATHS
-		/usr/local/include/${libname2}
-		/usr/include/${libname2}
-		/system/develop/headers/${libname2} #Haiku
-		PATH_SUFFIXES "include/${libname2}"
-	)
-
-	if(IRRLICHT_INCLUDE_DIR)
-		break()
-	endif()
-endforeach()
+find_path(IRRLICHT_INCLUDE_DIR NAMES irrlicht.h
+	DOC "Path to the directory with IrrlichtMt includes"
+	PATHS
+	/usr/local/include/irrlichtmt
+	/usr/include/irrlichtmt
+	/system/develop/headers/irrlichtmt #Haiku
+	PATH_SUFFIXES "include/irrlichtmt"
+)
 
 # Handholding for users
 if(IRRLICHT_INCLUDE_DIR AND (NOT IS_DIRECTORY "${IRRLICHT_INCLUDE_DIR}" OR

util/ci/common.sh

@@ -9,9 +9,6 @@ install_linux_deps() {
 
 	if [[ "$1" == "--no-irr" ]]; then
 		shift
-	elif [[ "$1" == "--old-irr" ]]; then
-		shift
-		pkgs+=(libirrlicht-dev)
 	else
 		wget "https://github.com/minetest/irrlicht/releases/download/1.9.0mt6/ubuntu-bionic.tar.gz"
 		sudo tar -xaf ubuntu-bionic.tar.gz -C /usr/local