use system provided ccache links

Change-Id: I0860bbd0cf368fc3638b861504ebf642ee9d3807
Signed-off-by: Damjan Marion <damarion@cisco.com>
diff --git a/build-root/build-config.mk b/build-root/build-config.mk
new file mode 100644
index 0000000..63683e0
--- /dev/null
+++ b/build-root/build-config.mk
@@ -0,0 +1 @@
+SOURCE_PATH = $(CURDIR)/..