Fix redirecting location of pdb via CMAKE_PDB_OUTPUT_DIRECTORY.

CMakeLists.txt

@@ -728,8 +728,10 @@ if(MSVC)
             ARCHIVE DESTINATION lib
             PUBLIC_HEADER DESTINATION include
             COMPONENT SDK)
-    install(FILES ${CMAKE_CURRENT_BINARY_DIR}/bin/libzmq-${CMAKE_VS_PLATFORM_TOOLSET}-mt-gd-${ZMQ_VERSION_MAJOR}_${ZMQ_VERSION_MINOR}_${ZMQ_VERSION_PATCH}.pdb DESTINATION lib
+    if(NOT CMAKE_PDB_OUTPUT_DIRECTORY)
+      install(FILES ${CMAKE_CURRENT_BINARY_DIR}/bin/libzmq-${CMAKE_VS_PLATFORM_TOOLSET}-mt-gd-${ZMQ_VERSION_MAJOR}_${ZMQ_VERSION_MINOR}_${ZMQ_VERSION_PATCH}.pdb DESTINATION lib
             COMPONENT SDK)
+    endif()
   else()
     install(TARGETS libzmq
             RUNTIME DESTINATION bin