cmake: always depend on threads, not only in the xmp case

CMakeLists.txt

@@ -120,7 +120,6 @@ IF( EXIV2_ENABLE_XMP )
     IF (NOT MINGW)
         set(THREADS_PREFER_PTHREAD_FLAG ON)
     ENDIF()
-    find_package(Threads REQUIRED)
 ENDIF( EXIV2_ENABLE_XMP )
 
 INCLUDE( config/CMakeChecks.txt )

config/CMakeChecks.txt

@@ -51,6 +51,8 @@ INCLUDE_DIRECTORIES( ${CMAKE_INCLUDE_PATH} ${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_C
 LINK_DIRECTORIES( ${CMAKE_LIBRARY_PATH} )
 SET( CMAKE_REQUIRED_INCLUDES ${CMAKE_INCLUDE_PATH} )
 
+find_package(Threads REQUIRED)
+
 IF( EXIV2_ENABLE_PNG )
     FIND_PACKAGE( ZLIB REQUIRED )
     INCLUDE_DIRECTORIES( ${ZLIB_INCLUDE_DIR} )

src/CMakeLists.txt

@@ -268,10 +268,12 @@ else()
         TARGET_LINK_LIBRARIES( exiv2lib ${PRIVATE_VAR} dl ${EXPAT_LIBRARIES} )
         TARGET_LINK_LIBRARIES( exiv2lib ${PRIVATE_VAR} dl ${CURL_LIBRARIES} )
         TARGET_LINK_LIBRARIES( exiv2lib ${PRIVATE_VAR} dl ${SSH_LIBRARIES} )
+        TARGET_LINK_LIBRARIES( exiv2lib ${PRIVATE_VAR} dl ${CMAKE_THREAD_LIBS_INIT} )
     else()
         TARGET_LINK_LIBRARIES( exiv2lib ${PRIVATE_VAR} ${EXPAT_LIBRARIES} )
         TARGET_LINK_LIBRARIES( exiv2lib ${PRIVATE_VAR} ${CURL_LIBRARIES} )
         TARGET_LINK_LIBRARIES( exiv2lib ${PRIVATE_VAR} ${SSH_LIBRARIES} )
+        TARGET_LINK_LIBRARIES( exiv2lib ${PRIVATE_VAR} ${CMAKE_THREAD_LIBS_INIT} )
     endif()
 endif()