Update Clang toolchain to match chromium's

Regular update to match chromium toolchain versions.

Change-Id: I2f96392db0c0e56c165db6ad6136103dca2df8cb
diff --git a/gn/standalone/BUILD.gn b/gn/standalone/BUILD.gn
index ffe5725..6660963 100644
--- a/gn/standalone/BUILD.gn
+++ b/gn/standalone/BUILD.gn
@@ -81,6 +81,7 @@
       "-Wno-padded",
       "-Wno-poison-system-directories",
       "-Wno-reserved-id-macro",
+      "-Wno-reserved-identifier",
       "-Wno-unknown-sanitizers",
       "-Wno-unknown-warning-option",
     ]