Build: allow multiple link time dependencies

Append to the `LINK_DEPENDS` property in `target_add_scatter_file` to
allow multiple dependencies for linking a target.

Change-Id: I294258fb5c5a799691f3ff340ebd9ee183809bbf
Signed-off-by: Anubhav Raina <anubhav.raina@arm.com>
diff --git a/toolchain_GNUARM.cmake b/toolchain_GNUARM.cmake
index 6c62ba7..2c52c99 100644
--- a/toolchain_GNUARM.cmake
+++ b/toolchain_GNUARM.cmake
@@ -258,7 +258,7 @@
         ${target}_scatter
     )
 
-    set_target_properties(${target} PROPERTIES LINK_DEPENDS $<TARGET_OBJECTS:${target}_scatter>)
+    set_property(TARGET ${target} APPEND PROPERTY LINK_DEPENDS $<TARGET_OBJECTS:${target}_scatter>)
 
     target_link_libraries(${target}_scatter
         platform_region_defs