Support finding both debug and optimized pthread libraries

CMake/FindPThreads.cmake

 find_path(PTHREAD_INCLUDE_DIR
     pthread.h
     )
+set(PTHREAD_INCLUDE_DIR ${PTHREAD_INCLUDE_DIR})
 
-find_library(PTHREAD_LIBRARY
+find_library(PTHREAD_RELEASE_LIBRARY
   NAMES
     pthread
     libpthread
     )
-
-set(PTHREAD_INCLUDE_DIRS "${PTHREAD_INCLUDE_DIR}")
-set(PTHREAD_LIBRARIES "${PTHREAD_LIBRARY}")
+if (EXISTS ${PTHREAD_RELEASE_LIBRARY})
+  list(APPEND PTHREAD_LIBRARIES optimized ${PTHREAD_RELEASE_LIBRARY})
+endif()
+find_library(PTHREAD_DEBUG_LIBRARY
+  NAMES
+    pthreadd
+    libpthreadd
+    )
+if (EXISTS ${PTHREAD_DEBUG_LIBRARY})
+  list(APPEND PTHREAD_LIBRARIES debug ${PTHREAD_DEBUG_LIBRARY})
+endif()
 
 include(FindPackageHandleStandardArgs)
 find_package_handle_standard_args(PTHREAD
   REQUIRED_VARS
     PTHREAD_INCLUDE_DIR
-    PTHREAD_LIBRARY)
+    PTHREAD_LIBRARIES)
 
 mark_as_advanced(
   PTHREAD_INCLUDE_DIR
-  PTHREAD_LIBRARY)
+  PTHREAD_DEBUG_LIBRARY
+  PTHREAD_RELEASE_LIBRARY)
 
 if(PTHREAD_FOUND AND NOT TARGET Threads::Threads)
   add_library(Threads::Threads INTERFACE IMPORTED)
-  set_target_properties(Threads::Threads PROPERTIES
-    INTERFACE_LINK_LIBRARIES "${PTHREAD_LIBRARY}"
-    INTERFACE_INCLUDE_DIRECTORIES "${PTHREAD_INCLUDE_DIRS}")
+  target_include_directories(Threads::Threads INTERFACE "${PTHREAD_INCLUDE_DIR}")
+  if (EXISTS ${PTHREAD_DEBUG_LIBRARY})
+    target_link_libraries(Threads::Threads INTERFACE debug ${PTHREAD_DEBUG_LIBRARY})
+  endif()
+  if (EXISTS ${PTHREAD_RELEASE_LIBRARY})
+    target_link_libraries(Threads::Threads INTERFACE optimized ${PTHREAD_RELEASE_LIBRARY})
+  endif()
 endif()