[cmake] Fix for system-installed boost.

scripts/cmake/Dependencies.cmake

@@ -190,27 +190,35 @@ if(OGS_USE_MFRONT)
  endif()
 endif()
 
+# Boost libraries used by ogs, can be linked with Boost::[lib_name]
+set(BOOST_INCLUDE_LIBRARIES
+ math
+ property_tree
+ algorithm
+ smart_ptr
+ tokenizer
+ assign
+ dynamic_bitset
+ range
+ variant
+)
 if(GUIX_BUILD)
  find_package(Boost REQUIRED)
 else()
- # Boost libraries used by ogs, can be linked with Boost::[lib_name]
- set(BOOST_INCLUDE_LIBRARIES
- math
- property_tree
- algorithm
- smart_ptr
- tokenizer
- assign
- dynamic_bitset
- range
- )
  CPMFindPackage(
  NAME Boost
  VERSION ${ogs.minimum_version.boost}
  URL https://github.com/boostorg/boost/releases/download/boost-${ogs.minimum_version.boost}/boost-${ogs.minimum_version.boost}.tar.xz
  OPTIONS "BOOST_ENABLE_CMAKE ON"
  )
 endif()
+if(NOT Boost_ADDED)
+ # Boost from system found. There are only Boost::headers and Boost::boost
+ # targets.
+ foreach(lib ${BOOST_INCLUDE_LIBRARIES})
+ add_library(Boost::${lib} ALIAS Boost::headers)
+ endforeach()
+endif()
 
 CPMFindPackage(
  NAME LibXml2