Set up rules to build static libraries for TARGET_2ND_ARCH

The rules for the 2nd arch are set up in the second inclusion
of static_library_internal.mk.
libfoo of the 2nd arch will be built into
$(PRODUCT_OUT)/obj_$(TARGET_2ND_ARCH)/libfoo_intermediates/libfoo.a.

Bug: 11654773
Change-Id: I1d92733968fc442e9225b4df5bd1b551a81d89f7
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 7b3ab31..9833a4a 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -142,6 +142,7 @@
 LOCAL_HAL_STATIC_LIBRARIES:=
 LOCAL_NO_SYNTAX_CHECK:=
 LOCAL_NO_STATIC_ANALYZER:=
+LOCAL_2ND_ARCH_VAR_PREFIX:=
 
 # Trim MAKEFILE_LIST so that $(call my-dir) doesn't need to
 # iterate over thousands of entries every time.