Support linking against NDK prebuilt libraries

When sdk_version is specified, we need to use the prebuilt ndk versions
of these libraries instead of the platform versions.

Change-Id: I4ff33a234a985041ebe11ab148d64d0f8df66fc4
diff --git a/cc/makevars.go b/cc/makevars.go
index f2214a2..a4fe077 100644
--- a/cc/makevars.go
+++ b/cc/makevars.go
@@ -40,6 +40,7 @@
 	ctx.Strict("GLOBAL_CLANG_CFLAGS_NO_OVERRIDE", "${clangExtraNoOverrideCflags}")
 	ctx.Strict("GLOBAL_CPPFLAGS_NO_OVERRIDE", "")
 	ctx.Strict("GLOBAL_CLANG_CPPFLAGS_NO_OVERRIDE", "")
+	ctx.Strict("NDK_PREBUILT_SHARED_LIBRARIES", strings.Join(ndkPrebuiltSharedLibs, " "))
 
 	hostTargets := ctx.Config().Targets[android.Host]
 	makeVarsToolchain(ctx, "", hostTargets[0])