[flang][cuda] Update syncthreads interface (#138023)

Author: clementval

flang/module/cudadevice.f90

@@ -17,9 +17,8 @@ module cudadevice
 
   ! Synchronization Functions
 
-  interface
-    attributes(device) subroutine syncthreads()
-    end subroutine
+  interface syncthreads
+    procedure :: syncthreads
   end interface
 
   interface
@@ -1614,4 +1613,9 @@ attributes(device,host) logical function on_device() bind(c)
     end function
   end interface
 
+contains
+
+  attributes(device) subroutine syncthreads()
+  end subroutine
+
 end module