Remove -pthread argument.

CMakeLists.txt

@@ -65,7 +65,6 @@ if(HAIKU)
 endif()
 
 if(UNIX AND NOT WINDOWS AND NOT APPLE)  # (MingW and such might be UNIX _and_ WINDOWS!)
-    set(OTHER_LDFLAGS ${OTHER_LDFLAGS} "-pthread")
     find_library(PTHREAD_LIBRARY pthread)
     if(PTHREAD_LIBRARY)
         set(OPTIONAL_LIBRARY_LIBS ${OPTIONAL_LIBRARY_LIBS} ${PTHREAD_LIBRARY})