Disable Precompile-platform with clang-cl.

third_party/WebKit/Source/core/BUILD.gn

Index: third_party/WebKit/Source/core/BUILD.gn
diff --git a/third_party/WebKit/Source/core/BUILD.gn b/third_party/WebKit/Source/core/BUILD.gn
index 0c58627a1145a40ced541856118442d19135c7d8..59bbee0defdc5ca8aa556137c48edda9ce55273f 100644
--- a/third_party/WebKit/Source/core/BUILD.gn
+++ b/third_party/WebKit/Source/core/BUILD.gn
@@ -52,7 +52,8 @@ import("//build/config/pch.gni")
 
 config("blink_core_pch") {
   if (enable_precompiled_headers) {
-    if (is_win) {
+    # TODO(thakis): Enable for clang once it works, https://crbug.com/667891
+    if (is_win && !is_clang) {
       # This is a string rather than a file GN knows about. It has to match
       # exactly what's in the /FI flag below, and what might appear in the
       # source code in quotes for an #include directive.