Reenable the removed-STL diagnostic

In r17, ndk-stl-check allowed deprecated STLs, and this diagnostic was a
warning. In r18, it should be an error instead, but it's currently disabled
because ndk-stl-check has aborted before we can issue it.

Changes:

Android NDK: Invalid APP_STL value: gnustl_static
Android NDK: Please use one of the following instead:  none system c++_static c++_shared
/path/to/add-application.mk:177: *** Android NDK: Aborting    .  Stop.

into:

/path/to/add-application.mk:178: *** Android NDK: APP_STL gnustl_static is no longer supported. Please switch to either c++_static or c++_shared. See https://developer.android.com/ndk/guides/cpp-support.html for more information.    .  Stop.

Test: manual
Test: ./checkbuild.py && ./run_tests.py
Bug: http://b/73980790#comment4
Change-Id: I89ba485190008d7e50ffd4f7e3e19a7909eb3114
diff --git a/build/core/add-application.mk b/build/core/add-application.mk
index a909c62..984585b 100644
--- a/build/core/add-application.mk
+++ b/build/core/add-application.mk
@@ -174,16 +174,15 @@
 ifndef APP_STL
     APP_STL := system
 else
+    ifneq ($(filter $(APP_STL),gnustl_static gnustl_shared stlport_static stlport_shared),)
+        $(call __ndk_error,APP_STL $(APP_STL) is no longer supported. Please \
+            switch to either c++_static or c++_shared. See \
+            https://developer.android.com/ndk/guides/cpp-support.html for more \
+            information.)
+    endif
     $(call ndk-stl-check,$(APP_STL))
 endif
 
-ifneq ($(filter $(APP_STL),gnustl_static gnustl_shared stlport_static stlport_shared),)
-    $(call __ndk_error,APP_STL $(APP_STL) is no longer supported. Please \
-        switch to either c++_static or c++_shared. See \
-        https://developer.android.com/ndk/guides/cpp-support.html for more \
-        information.)
-endif
-
 # wrap.sh files can be specified in the user's Application.mk in either an
 # ABI-generic (APP_WRAP_SH) or ABI-specific (APP_WRAP_SH_x86, etc) fashion.
 # These two approaches cannot be combined; if any ABI-specific wrap.sh files are