Switch to clang-3859424.

Bug: http://b/36442361
Test: Build and run multiple devices/targets.

(cherry picked from commit 4442c2f98e)

Change-Id: I3e870a2fa1933e5f36f328bf6e3a707c8b2f661f

cc/config/global.go

@@ -132,7 +132,7 @@ func init() {
 		if override := config.(android.Config).Getenv("LLVM_PREBUILTS_VERSION"); override != "" {
 			return override, nil
 		}
-		return "clang-3688880", nil
+		return "clang-3859424", nil
 	})
 	pctx.StaticVariable("ClangPath", "${ClangBase}/${HostPrebuiltTag}/${ClangVersion}")
 	pctx.StaticVariable("ClangBin", "${ClangPath}/bin")