Modernise Boost CMake stuff

Resolves https://gitlab.com/OpenMW/openmw/-/issues/8100

Also removes some old crud.
Hopefully the old crud is all:
* Handled automatically by CMake now we're using the modern approach.
* A hack-fix for a problem caused by not using the modern approach.
* Massively outdated so no longer necessary.

If it turns out this makes CI fail, I'll tweak things as necessary.

Changes that might not be wanted include:
* Getting rid of our BOOST_STATIC CMake option. In cases where the CMake config doesn't make the one correct choice from the build environment (i.e. because there's a choice) the CMake config exposes the option already.
  However, we were forcing this on for Windows, so that might matter.
  It seems to default to static on my machine even though I thought I read something suggesting otherwise, so we'll see how things go with that.
  If we eventually put CMake in charge of installing dependency DLLs this will be a moot point as we won't need to care.
* Bumping the minimum version of Boost to 1.70.0, as that's the first with working CMake config.
  It's from 2019, so plausibly there are distros too scared to use a library from five years ago as it can't legally drink in the US (although it could in limited quantities with parental supervision in the UK, as long as it's just something inconsequential like a single sip of beer).

CI/before_script.msvc.sh

@@ -713,9 +713,7 @@ printf "Boost ${BOOST_VER}... "
 			"${DEPS}/boost-${BOOST_VER}-msvc${MSVC_VER}-win${BITS}.exe" //DIR="${CWD_DRIVE_ROOT}" //VERYSILENT //NORESTART ${CI_EXTRA_INNO_OPTIONS}
 			mv "${CWD_DRIVE_ROOT_BASH}" "${BOOST_SDK}"
 		fi
-		add_cmake_opts -DBOOST_ROOT="$BOOST_SDK" \
-			-DBOOST_LIBRARYDIR="${BOOST_SDK}/lib${BITS}-msvc-${MSVC_VER}"
-		add_cmake_opts -DBoost_COMPILER="-${TOOLSET}"
+		BOOST_PREFIX="${BOOST_SDK}/lib${BITS}-msvc-${MSVC_VER}/cmake/Boost-1.80.0"
 		echo Done.
 }
 cd $DEPS
@@ -1028,7 +1026,7 @@ printf "zlib 1.2.11... "
 	echo Done.
 }
 
-add_cmake_opts -DCMAKE_PREFIX_PATH="\"${QT_SDK};${SDL2DIR}\""
+add_cmake_opts -DCMAKE_PREFIX_PATH="\"${QT_SDK};${SDL2DIR};${BOOST_PREFIX}\""
 
 echo
 cd $DEPS_INSTALL/..

CMakeLists.txt

@@ -124,7 +124,6 @@ include(WholeArchive)
 
 configure_file ("${OpenMW_SOURCE_DIR}/docs/mainpage.hpp.cmake" "${OpenMW_BINARY_DIR}/docs/mainpage.hpp")
 
-option(BOOST_STATIC "Link static build of Boost into the binaries" FALSE)
 option(QT_STATIC "Link static build of Qt into the binaries" FALSE)
 
 option(OPENMW_USE_SYSTEM_BULLET "Use system provided bullet physics library" ON)
@@ -369,11 +368,6 @@ endif()
 
 # Platform specific
 if (WIN32)
-    if(NOT MINGW)
-    set(Boost_USE_STATIC_LIBS   ON)
-    add_definitions(-DBOOST_ALL_NO_LIB)
-    endif(NOT MINGW)
-
     # Suppress WinMain(), provided by SDL
     add_definitions(-DSDL_MAIN_HANDLED)
 
@@ -466,14 +460,7 @@ if(WIN32)
     endif(MSVC)
 endif(WIN32)
 
-IF(BOOST_STATIC)
-    set(Boost_USE_STATIC_LIBS   ON)
-endif()
-
-set(Boost_NO_BOOST_CMAKE ON)
-set(Boost_NO_WARN_NEW_VERSIONS ON)  # ignore warnings about new releases of boost
-
-find_package(Boost 1.6.2 REQUIRED COMPONENTS ${BOOST_COMPONENTS} OPTIONAL_COMPONENTS ${BOOST_OPTIONAL_COMPONENTS})
+find_package(Boost 1.70.0 CONFIG REQUIRED COMPONENTS ${BOOST_COMPONENTS} OPTIONAL_COMPONENTS ${BOOST_OPTIONAL_COMPONENTS})
 
 if(OPENMW_USE_SYSTEM_MYGUI)
     find_package(MyGUI 3.4.3 REQUIRED)
@@ -502,7 +489,6 @@ set(SOL_CONFIG_DIR ${OpenMW_SOURCE_DIR}/extern/sol_config)
 include_directories(
     BEFORE SYSTEM
     "."
-    ${Boost_INCLUDE_DIR}
     ${MyGUI_INCLUDE_DIRS}
     ${OPENAL_INCLUDE_DIR}
     ${OPENGL_INCLUDE_DIR}
@@ -513,7 +499,7 @@ include_directories(
     ${ICU_INCLUDE_DIRS}
 )
 
-link_directories(${Boost_LIBRARY_DIRS} ${COLLADA_DOM_LIBRARY_DIRS})
+link_directories(${COLLADA_DOM_LIBRARY_DIRS})
 
 if(MYGUI_STATIC)
     add_definitions(-DMYGUI_STATIC)
@@ -601,7 +587,6 @@ endif()
 
 if (CMAKE_CXX_COMPILER_ID STREQUAL GNU OR CMAKE_CXX_COMPILER_ID STREQUAL Clang)
     set(OPENMW_CXX_FLAGS "-Wall -Wextra -Wundef -Wextra-semi -Wno-unused-parameter -pedantic -Wno-long-long -Wnon-virtual-dtor -Wunused ${OPENMW_CXX_FLAGS}")
-    add_definitions( -DBOOST_NO_CXX11_SCOPED_ENUMS=ON )
 
     if (APPLE)
         set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -stdlib=libc++")

apps/bsatool/CMakeLists.txt

@@ -9,7 +9,7 @@ openmw_add_executable(bsatool
 )
 
 target_link_libraries(bsatool
-    ${Boost_PROGRAM_OPTIONS_LIBRARY}
+    Boost::program_options
     components
 )
 

apps/bulletobjecttool/CMakeLists.txt

@@ -6,7 +6,7 @@ source_group(apps\\bulletobjecttool FILES ${BULLETMESHTOOL})
 openmw_add_executable(openmw-bulletobjecttool ${BULLETMESHTOOL})
 
 target_link_libraries(openmw-bulletobjecttool
-    ${Boost_PROGRAM_OPTIONS_LIBRARY}
+    Boost::program_options
     components
 )
 

apps/esmtool/CMakeLists.txt

@@ -16,7 +16,7 @@ openmw_add_executable(esmtool
 )
 
 target_link_libraries(esmtool
-    ${Boost_PROGRAM_OPTIONS_LIBRARY}
+    Boost::program_options
     components
 )
 

apps/essimporter/CMakeLists.txt

@@ -34,7 +34,7 @@ openmw_add_executable(openmw-essimporter
 )
 
 target_link_libraries(openmw-essimporter
-    ${Boost_PROGRAM_OPTIONS_LIBRARY}
+    Boost::program_options
     components
 )
 

apps/mwiniimporter/CMakeLists.txt

@@ -14,13 +14,13 @@ openmw_add_executable(openmw-iniimporter
 )
 
 target_link_libraries(openmw-iniimporter
-    ${Boost_PROGRAM_OPTIONS_LIBRARY}
+    Boost::program_options
     components
 )
 
 if (WIN32)
     target_link_libraries(openmw-iniimporter
-    ${Boost_LOCALE_LIBRARY})
+        Boost::locale)
     INSTALL(TARGETS openmw-iniimporter RUNTIME DESTINATION ".")
 endif(WIN32)
 

apps/navmeshtool/CMakeLists.txt

@@ -8,7 +8,7 @@ source_group(apps\\navmeshtool FILES ${NAVMESHTOOL})
 openmw_add_executable(openmw-navmeshtool ${NAVMESHTOOL})
 
 target_link_libraries(openmw-navmeshtool
-    ${Boost_PROGRAM_OPTIONS_LIBRARY}
+    Boost::program_options
     components
 )
 

apps/opencs/CMakeLists.txt

@@ -244,7 +244,7 @@ target_link_libraries(openmw-cs-lib
     ${OSGTEXT_LIBRARIES}
     ${OSG_LIBRARIES}
     ${EXTERN_OSGQT_LIBRARY}
-    ${Boost_PROGRAM_OPTIONS_LIBRARY}
+    Boost::program_options
     components_qt
 )
 
@@ -255,7 +255,7 @@ else()
 endif()
 
 if (WIN32)
-    target_link_libraries(openmw-cs-lib ${Boost_LOCALE_LIBRARY})
+    target_link_libraries(openmw-cs-lib Boost::locale)
     target_sources(openmw-cs PRIVATE ${CMAKE_SOURCE_DIR}/files/windows/openmw-cs.exe.manifest)
 endif()
 

apps/openmw/CMakeLists.txt

@@ -159,7 +159,7 @@ target_link_libraries(openmw-lib
     ${OSGDB_LIBRARIES}
     ${OSGUTIL_LIBRARIES}
     ${OSG_LIBRARIES}
-    ${Boost_PROGRAM_OPTIONS_LIBRARY}
+    Boost::program_options
     ${OPENAL_LIBRARY}
     ${FFmpeg_LIBRARIES}
     ${MyGUI_LIBRARIES}

components/CMakeLists.txt

@@ -586,9 +586,9 @@ target_link_libraries(components
     ${OSG_LIBRARIES}
     ${OPENTHREADS_LIBRARIES}
 
-    ${Boost_SYSTEM_LIBRARY}
-    ${Boost_PROGRAM_OPTIONS_LIBRARY}
-    ${Boost_IOSTREAMS_LIBRARY}
+    Boost::system
+    Boost::program_options
+    Boost::iostreams
 
     SDL2::SDL2
     ${OPENGL_gl_LIBRARY}
@@ -612,16 +612,12 @@ else()
     target_link_libraries(components yaml-cpp)
 endif()
 
-if(Boost_VERSION_STRING VERSION_GREATER_EQUAL 1.77.0)
-    target_link_libraries(components ${Boost_ATOMIC_LIBRARY})
-endif()
-
 target_link_libraries(components ${BULLET_LIBRARIES})
 
 if (WIN32)
     target_link_libraries(components
-    ${Boost_LOCALE_LIBRARY}
-    ${Boost_ZLIB_LIBRARY})
+    Boost::locale
+    Boost::zlib)
 endif()
 
 if (USE_QT)