make: Add support to skip current VNDK install

You can get a system.img without current VNDK libs.
This may help when you want a smaller system.img given that the image
will be used with a specific version (not current) of vendor image.

Bug: 132140714
Test: m TARGET_SKIP_CURRENT_VNDK=true && see if current VNDK is not
installed

Change-Id: Ie0815e6dd6ce2f861b6c42e637da4bb146320673
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index fafdce6..5973e0e 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -269,6 +269,7 @@
 LOCAL_SOONG_SYMBOL_PATH :=
 LOCAL_SOONG_TOC :=
 LOCAL_SOONG_UNSTRIPPED_BINARY :=
+LOCAL_SOONG_VNDK_VERSION :=
 # '',true
 LOCAL_SOURCE_FILES_ALL_GENERATED:=
 LOCAL_SRC_FILES:=