Add the sdk_version that this should be built against.

Setting this enables our testing tools that must be SDK/NDK
compliant to include these static libs in their builds.

Bug: 74442448
Test: compile and CtsSkQPTestCases
Change-Id: If5e9da6392999767f7aec717d5c928bfb45385fc
diff --git a/Android.bp b/Android.bp
index d54c879..737a3c2 100644
--- a/Android.bp
+++ b/Android.bp
@@ -109,6 +109,8 @@
     local_include_dirs: ["."],
     static_libs: ["webp-headers"],
     export_static_lib_headers: ["webp-headers"],
+
+    sdk_version: "9",
 }
 
 //##############################################