Allow to force min sdk given to Jack

Allows setting the min sdk version for target Jack commands,
overriding the default value obtained from LOCAL_SDK_CURRENT.

Bug: 28188420

(cherry picked from commit 109141ccc97d27cfc72affe3c45f3e6c2fb89702)

Change-Id: Id9c5275bc71b8d9042173bf1e40aa3199e9508e6
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 9c2fa1d..7473a73 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -116,6 +116,7 @@
 LOCAL_JILL_FLAGS:=
 LOCAL_CERTIFICATE:=
 LOCAL_SDK_VERSION:=
+LOCAL_MIN_SDK_VERSION:=
 LOCAL_SDK_RES_VERSION:=
 LOCAL_NDK_STL_VARIANT:=
 LOCAL_EMMA_INSTRUMENT:=