Switch libunwind_llvm over to building for NDK 21.
am: d9a5f194c9

Change-Id: I1caa3593bc0c6041fd4340b63f922eab9ef4d698
diff --git a/Android.bp b/Android.bp
index 1c89df4..a256b4f 100644
--- a/Android.bp
+++ b/Android.bp
@@ -45,6 +45,7 @@
 cc_library_static {
     name: "libunwind_llvm",
     clang: true,
+    sdk_version: "21",
     srcs: LIBUNWIND_SRC_FILES,
     include_dirs: LIBUNWIND_INCLUDES,
     local_include_dirs: LIBUNWIND_LOCAL_INCLUDES,