Add new variable SCAN_EXCLUDE_DIRS; specifies directories to exclude when searching source tree.

These directories are excluded in addition to OUT_DIR.
This can be useful if your build system has other output directories
beyond what OUT_DIR is set to.

Change-Id: I6d98a85bcc8c89279e939406a7fec32547e8922f
diff --git a/core/config.mk b/core/config.mk
index bfa5610..e6a6812 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -150,6 +150,10 @@
 # are specific to the user's build configuration.
 include $(BUILD_SYSTEM)/envsetup.mk
 
+# Pruned directory options used when using findleaves.py
+# See envsetup.mk for a description of SCAN_EXCLUDE_DIRS
+FIND_LEAVES_EXCLUDES := $(addprefix --prune=, $(OUT_DIR) $(SCAN_EXCLUDE_DIRS) .repo .git)
+
 # The build system exposes several variables for where to find the kernel
 # headers:
 #   TARGET_DEVICE_KERNEL_HEADERS is automatically created for the current