Unconditionally enable LTO in linker (#6350)

Co-authored-by: Amaury Chamayou <[email protected]>

CHANGELOG.md

@@ -13,6 +13,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - The `cchost` configuration file now includes an `idle_connection_timeout` option. This controls how long the node will keep idle connections (for user TLS sessions) before automatically closing them. This may be set to `null` to restore the previous behaviour, where idle connections are never closed. By default connections will be closed after 60s of idle time.
 
+### Changed
+
+- Set LTO on for both debug/release linkages to support linking against CCF libraries if the client code has been built in debug mode.
+
 ## [5.0.0-rc0]
 
 [5.0.0-rc0]: https://github.com/microsoft/CCF/releases/tag/ccf-5.0.0-rc0

cmake/preproject.cmake

@@ -90,8 +90,10 @@ endif()
 if("${COMPILE_TARGET}" STREQUAL "snp" OR "${COMPILE_TARGET}" STREQUAL "virtual")
   if(NOT "${CMAKE_BUILD_TYPE}" STREQUAL "Debug" AND NOT TSAN)
     add_compile_options(-flto)
-    add_link_options(-flto)
   endif()
+  # Unconditionally make linker aware of possible LTO happening. Otherwise
+  # targets built in Debug and linked against this will fail linkage.
+  add_link_options(-flto)
 endif()
 
 set(CMAKE_CXX_STANDARD 20)