Fix adb shell in 7.0 tree

busybox sh does not seem to work properly in 7.0 trees so use
mksh for sh instead.

Change-Id: Ia33bc3894f929b1348c8714d4ddd00a2671c7e94
diff --git a/prebuilt/Android.mk b/prebuilt/Android.mk
index 169f87f..a81781b 100644
--- a/prebuilt/Android.mk
+++ b/prebuilt/Android.mk
@@ -17,6 +17,9 @@
 RELINK_SOURCE_FILES += $(TARGET_RECOVERY_ROOT_OUT)/sbin/bu
 ifneq ($(TW_USE_TOOLBOX), true)
 	RELINK_SOURCE_FILES += $(TARGET_OUT_OPTIONAL_EXECUTABLES)/busybox
+	ifeq ($(shell test $(PLATFORM_SDK_VERSION) -ge 24; echo $$?),0)
+		RELINK_SOURCE_FILES += $(TARGET_OUT_EXECUTABLES)/sh
+	endif
 else
 	RELINK_SOURCE_FILES += $(TARGET_OUT_EXECUTABLES)/sh
 	RELINK_SOURCE_FILES += $(TARGET_OUT_SHARED_LIBRARIES)/libcrypto.so