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/gui/Android.mk b/gui/Android.mk
index 3f97ca7..b514e5b 100644
--- a/gui/Android.mk
+++ b/gui/Android.mk
@@ -173,8 +173,10 @@
 	cp -fr $(TWRP_THEME_LOC)/* $(TARGET_RECOVERY_ROOT_OUT)$(TWRES_PATH)
 	mkdir -p $(TARGET_RECOVERY_ROOT_OUT)/sbin/
 ifneq ($(TW_USE_TOOLBOX), true)
+ifeq ($(shell test $(PLATFORM_SDK_VERSION) -lt 24; echo $$?),0)
 	ln -sf $(TWRP_SH_TARGET) $(TARGET_RECOVERY_ROOT_OUT)/sbin/sh
 endif
+endif
 	ln -sf /sbin/pigz $(TARGET_RECOVERY_ROOT_OUT)/sbin/gzip
 	ln -sf /sbin/unpigz $(TARGET_RECOVERY_ROOT_OUT)/sbin/gunzip