Remove custom Boost finding logic, rely on CONFIG mode.

CMakeLists.txt

@@ -164,7 +164,20 @@ endif()
 find_package(absl REQUIRED)
 
 # Boost setup.
-include(ObakeFindBoost)
+# NOTE: stacktrace available since 1.65.0.
+set(_OBAKE_MIN_BOOST_VERSION "1.69")
+# NOTE: we look for Boost in CONFIG mode first, as that has become the official supported way
+# of locating Boost in recent Boost/CMake versions. If we fail, we try again in
+# MODULE mode as last resort.
+find_package(Boost ${_OBAKE_MIN_BOOST_VERSION} QUIET COMPONENTS serialization CONFIG)
+if(NOT ${Boost_FOUND})
+    message(STATUS "Boost not found in CONFIG mode, retrying in MODULE mode.")
+    find_package(Boost ${_OBAKE_MIN_BOOST_VERSION} QUIET MODULE COMPONENTS serialization)
+endif()
+if(NOT ${Boost_FOUND})
+    message(FATAL_ERROR "Could not locate Boost in either CONFIG or MODULE mode.")
+endif()
+message(STATUS "Found Boost version ${Boost_VERSION}.")
 
 # libbacktrace.
 if(OBAKE_WITH_LIBBACKTRACE)
@@ -421,7 +434,6 @@ install(FILES
     "${CMAKE_CURRENT_SOURCE_DIR}/cmake/FindDbgEng.cmake"
     "${CMAKE_CURRENT_SOURCE_DIR}/cmake/FindTBB.cmake"
     "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Findlibbacktrace.cmake"
-    "${CMAKE_CURRENT_SOURCE_DIR}/cmake/ObakeFindBoost.cmake"
     "${CMAKE_CURRENT_SOURCE_DIR}/cmake/ObakeFindDl.cmake"
 DESTINATION "${OBAKE_INSTALL_LIBDIR}/cmake/obake")
 install(EXPORT obake_export NAMESPACE obake:: DESTINATION "${OBAKE_INSTALL_LIBDIR}/cmake/obake")

obake-config.cmake.in

@@ -9,7 +9,6 @@ if(${mp++_VERSION} VERSION_LESS @_OBAKE_MIN_MPPP_VERSION@)
     message(FATAL_ERROR "The minimum mp++ version required by obake is @_OBAKE_MIN_MPPP_VERSION@, but version ${mp++_VERSION} was found instead.")
 endif()
 find_package(absl REQUIRED)
-include(ObakeFindBoost)
 # TBB. Try to find it first in config mode (supported
 # since version 2021 after the oneTBB rename), and, if this
 # fails, fall back to our own FindTBB.cmake. This is of course