Update conversion results file only when it changed.

Test: treehugger
Change-Id: Ia0d6bf614fa0714a977b2880f7271d54df034366

core/board_config.mk

diff --git a/core/board_config.mk b/core/board_config.mk
index b3e6957..120f511 100644
--- a/core/board_config.mk
+++ b/core/board_config.mk
@@ -214,10 +214,8 @@
     $(error board configuration converter failed: $(.SHELLSTATUS))
   endif
 
-  $(shell $(OUT_DIR)/soong/rbcrun \
-    RBC_OUT="make,global" \
-    $(OUT_DIR)/rbc/boardlauncher.rbc \
-    >$(OUT_DIR)/rbc/rbc_board_config_results.mk)
+  $(shell build/soong/scripts/update_out $(OUT_DIR)/rbc/rbc_board_config_results.mk \
+    $(OUT_DIR)/soong/rbcrun RBC_OUT="make,global" $(OUT_DIR)/rbc/boardlauncher.rbc)
   ifneq ($(.SHELLSTATUS),0)
     $(error board configuration runner failed: $(.SHELLSTATUS))
   endif

core/product_config.mk

diff --git a/core/product_config.mk b/core/product_config.mk
index 6588b8e..614dfa2 100644
--- a/core/product_config.mk
+++ b/core/product_config.mk
@@ -206,8 +206,8 @@
 ifndef RBC_PRODUCT_CONFIG
 $(call import-products, $(current_product_makefile))
 else
-  $(shell build/soong/scripts/rbc-run $(current_product_makefile) \
-      >$(OUT_DIR)/rbctemp.mk)
+  $(shell build/soong/scripts/update_out $(OUT_DIR)/rbctemp.mk \
+      build/soong/scripts/rbc-run $(current_product_makefile))
   ifneq ($(.SHELLSTATUS),0)
     $(error product configuration converter failed: $(.SHELLSTATUS))
   endif