[Mac/GN] Add a new linker_driver.py option to save unstripped linker output.

build/config/BUILDCONFIG.gn

Index: build/config/BUILDCONFIG.gn
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index db070eb750cff1783ba40ad12a982b29dd9ea825..c2112b9195110b0d979ec74380ff287c604426d0 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -529,7 +529,10 @@ if (is_win) {
     "//build/config/win:console",
   ]
 } else if (is_mac) {
-  _linker_configs = [ "//build/config/mac:strip_all" ]
+  _linker_configs = [
+    "//build/config/mac:strip_all",
+    "//build/config/mac:save_unstripped_output",

[brettw, 2016/07/18 17:53:00]

The only reason anything needs to be in the default configs list is if some
targets need to opt-out of that feature by removing the config.

It doesn't seem like this is the case for this feature. It looks reasonable to
modify the "strip_all" config to add the flag to additionally save unstripped
output given the build args. Does that look possible to you?

[Robert Sesek, 2016/07/18 18:46:10]

There are targets that opt out of strip_all because they need to customize the
arguments to strip (but the target does end up getting stripped). Those targets
will want the unstripped copy saved though, so having this be a separate config
allows them to remove strip_all but not the -Wcrl,unstripped flag.

+  ]
 } else {
   _linker_configs = []
 }