cmake: simplify libintl check

According to https://cmake.org/cmake/help/v3.4/module/FindIntl.html
the FindIntl module already checks for libintl.so.

config/CMakeChecks.txt

@@ -98,18 +98,11 @@ ENDIF( EXIV2_ENABLE_SHARED )
 
 IF( EXIV2_ENABLE_NLS )
     FIND_PACKAGE(Intl)
-    if(Intl_FOUND AND NOT MSVC)
+    if(Intl_FOUND)
         INCLUDE_DIRECTORIES(${Intl_INCLUDE_DIRS})
-        find_library(LIBINTL_LIBRARY NAMES intl libintl)
-        if(libintl_FOUND)
-            INCLUDE_DIRECTORIES(${Intl_INCLUDE_DIRS})
-            SET(LIBINTL_LIBRARIES ${LIBINTL_LIBRARY})
-        else()
-            SET(LIBINTL_LIBRARIES)
-            if ( APPLE OR CYGWIN )
-                SET(LIBINTL_LIBRARIES -lintl)
-            endif()
-        endif()
+        SET(LIBINTL_LIBRARIES ${Intl_LIBRARIES})
+    else()
+        SET(LIBINTL_LIBRARIES)
     endif()
     IF( NOT LOCALEDIR )
         SET( LOCALEDIR "${CMAKE_INSTALL_LOCALEDIR}" )