Roll Clang 214024:216630 (+216684) and switch to CMake (try 2)

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index d66f54c57a0c84cbe2f44c46f87d35a3d74eb599..b9e8e175de5400f984231f34d2a21bb6c2317834 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -109,6 +109,17 @@ config("compiler") {
       # and the fix is in chromium.
       "-fno-slp-vectorize",
     ]
+
+    if (is_debug) {
+      # Allow comparing the address of references and 'this' against 0
+      # in debug builds. Technically, these can never be null in
+      # well-defined C/C++ and Clang can optimize such checks away in
+      # release builds, but they may be used in asserts in debug builds.
+      cflags_cc += [
+        "-Wno-undefined-bool-conversion",
+        "-Wno-tautological-undefined-compare",
+      ]
+    }
   }
 
   if (is_clang && !is_win) {