Rebase CFLAGS and COPYING removal patch onto 1.13.0
Use CTest module for standard BUILD_TESTING switch and make Qt5Test optional

--- a/CMakeLists.txt	2017-08-28 21:43:54.000000000 +0200
+++ b/CMakeLists.txt	2021-02-27 19:21:04.090117623 +0100
@@ -57,6 +57,9 @@
 add_definitions(-DGLEW_STATIC)
 add_definitions(-DGLEW_NO_GLU)
 
+# Enable CMake's unit test framework
+include(CTest)
+
 if(UNIX)
     include("InstallLinux.cmake")
 elseif(WIN32)
@@ -64,8 +67,7 @@
 endif()
 
 if(CMAKE_COMPILER_IS_GNUCXX OR MINGW OR ${CMAKE_CXX_COMPILER_ID} STREQUAL "Clang")
-    add_compile_options(-std=c++11 -W -Wall -O3 -pedantic)
-    add_compile_options(-fomit-frame-pointer -finline-functions -ffast-math)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -W -Wall -fomit-frame-pointer -finline-functions")
 elseif(MSVC)
     add_definitions(-DNOMINMAX)
 endif()
@@ -83,7 +85,10 @@
 find_package(Qt5Xml ${QT_MIN_VER} REQUIRED)
 find_package(Qt5Widgets ${QT_MIN_VER} REQUIRED)
 find_package(Qt5LinguistTools ${QT_MIN_VER} REQUIRED)
-find_package(Qt5Test ${QT_MIN_VER} REQUIRED)
+
+if(BUILD_TESTING)
+    find_package(Qt5Test ${QT_MIN_VER} REQUIRED)
+endif()
 
 # Find OpenGL
 find_package(OpenGL REQUIRED)
@@ -109,9 +114,6 @@
     pkg_check_modules(VORBISFILE REQUIRED vorbisfile)
 endif()
 
-# Enable CMake's unit test framework
-enable_testing()
-
 # Install paths depend on the build type and target platform
 resolve_install_paths()
 
--- a/InstallLinux.cmake	2017-08-28 21:43:54.000000000 +0200
+++ b/InstallLinux.cmake	2021-02-27 19:21:23.760211724 +0100
@@ -58,7 +58,7 @@
     install(FILES data/fonts.conf DESTINATION ${DATA_PATH})
     install(FILES data/meshes.conf DESTINATION ${DATA_PATH})
     install(FILES data/surfaces.conf DESTINATION ${DATA_PATH})
-    install(FILES AUTHORS CHANGELOG COPYING README.md DESTINATION ${DOC_PATH})
+    install(FILES AUTHORS CHANGELOG README.md DESTINATION ${DOC_PATH})
     install(DIRECTORY data/images DESTINATION ${DATA_PATH} FILES_MATCHING PATTERN "*.jpg")
     install(DIRECTORY data/images DESTINATION ${DATA_PATH} FILES_MATCHING PATTERN "*.png")
     install(DIRECTORY data/levels DESTINATION ${DATA_PATH} FILES_MATCHING PATTERN "*.trk")
--- a/src/game/MiniCore/CMakeLists.txt	2017-08-28 21:43:54.000000000 +0200
+++ b/src/game/MiniCore/CMakeLists.txt	2021-02-27 19:17:29.616848751 +0100
@@ -86,5 +86,7 @@
 
 target_link_libraries(MiniCore Qt5::OpenGL Qt5::Xml)
 
-add_subdirectory(UnitTests)
+if(BUILD_TESTING)
+    add_subdirectory(UnitTests)
+endif()