Slightly easier debugging of missing inputs to copy-file-to-target

Test: call copy-file-to-target without any inputs and read the quoted output
Bug: 36792868
Change-Id: I3a78f7ae4535ffe100b72458a3494ee398daf732
diff --git a/core/definitions.mk b/core/definitions.mk
index 6199837..ed205d3 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -2805,7 +2805,7 @@
 define copy-file-to-target
 @mkdir -p $(dir $@)
 $(hide) rm -f $@
-$(hide) cp $< $@
+$(hide) cp "$<" "$@"
 endef
 
 # The same as copy-file-to-target, but use the local
@@ -2813,7 +2813,7 @@
 define copy-file-to-target-with-cp
 @mkdir -p $(dir $@)
 $(hide) rm -f $@
-$(hide) cp -p $< $@
+$(hide) cp -p "$<" "$@"
 endef
 
 # The same as copy-file-to-target, but strip out "# comment"-style