Move libc++ configs and flags out of //build/config/sanitizers

build/config/BUILDCONFIG.gn

Index: build/config/BUILDCONFIG.gn
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index 38a6119db8320b91b297458d77521a1465ccdacb..144aa3ac5c74336364d6ded1b03d1fe08e27c049 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -519,6 +519,7 @@ default_compiler_configs = [
   "//build/config/compiler:default_symbols",
   "//build/config/compiler:no_rtti",
   "//build/config/compiler:runtime_library",
+  "//build/config/libc++:libc++flags",

[brettw, 2017/06/12 17:55:18]

The reason things need to go here is that targets need to opt-out of them. Will
this need to happen? If this capability is not needed, it might be nice to
reference this from somewhere else like the "compiler" config.

[Tom Anderson, 2017/06/16 20:49:50]

I think (maybe) cronet needs to remove it so it can link against the system
libc++ instead

[brettw, 2017/06/19 23:40:26]

Your current patch doesn't implement this. Since we also aren't sure if it will
be necessary, I think we should not be modifying the file and do the sub-config
solution I suggested. Chronet people can move it to here if they need it.

   "//build/config/sanitizers:default_sanitizer_flags",
 ]
 if (is_win) {