Switch to clang-4630689

Bug: http://b/73127367
Bug: http://b/68659946

These new prebuilts have fixes for the bugs mentioned above.

Test: Build and verify that issues in both bugs above are fixed.
Change-Id: I410a43b70920d509118f8e6fdb012ef6b078d657
diff --git a/cc/config/global.go b/cc/config/global.go
index 55ae9e3..a7a2ea4 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -116,7 +116,7 @@
 
 	// prebuilts/clang default settings.
 	ClangDefaultBase         = "prebuilts/clang/host"
-	ClangDefaultVersion      = "clang-4579689"
+	ClangDefaultVersion      = "clang-4630689"
 	ClangDefaultShortVersion = "6.0.1"
 
 	// Directories with warnings from Android.bp files.