Use clang as default host compiler when cross-compiling

build/set_clang_warning_flags.gypi

Index: build/set_clang_warning_flags.gypi
diff --git a/build/set_clang_warning_flags.gypi b/build/set_clang_warning_flags.gypi
index 3fe75d6a6b12f60bdc28f74456b795893aca0ee2..f6d7aea700d8d568bcd2598eb39ce4e69d6bc1fc 100644
--- a/build/set_clang_warning_flags.gypi
+++ b/build/set_clang_warning_flags.gypi
@@ -46,5 +46,13 @@
         },
       },
     }],
+    ['clang==0 and host_clang==1', {
+      'target_conditions': [
+        ['_toolset=="host"', {
+          'cflags': [ '>@(clang_warning_flags)' ],
+          'cflags!': [ '>@(clang_warning_flags_unset)' ],
+        }],
+      ],
+    }],
   ],
 }