Fix linker issues using easylogging

external/easylogging++/CMakeLists.txt

@@ -33,6 +33,7 @@ project(easylogging CXX)
 SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
 
 find_package(Threads)
+find_package(Backtrace)
 
 add_library(easylogging
   easylogging++.cc)
@@ -41,7 +42,8 @@ include_directories("${CMAKE_CURRENT_SOURCE_DIR}")
 include_directories("${CMAKE_CURRENT_BINARY_DIR}")
 target_link_libraries(easylogging
   PRIVATE
-    ${CMAKE_THREAD_LIBS_INIT})
+    ${CMAKE_THREAD_LIBS_INIT}
+    ${Backtrace_LIBRARIES})
 
 # GUI/libwallet install target
 if (BUILD_GUI_DEPS)