[Chromecast] Don't use static c++ libraries for clang builds

build/config/chromecast/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/chromecast_build.gni")
 
 assert(is_chromecast)
 
 config("static_config") {
   ldflags = [
     # Don't allow visible symbols from libraries that contain
     # assembly code with symbols that aren't hidden properly.
     # http://b/26390825
     "-Wl,--exclude-libs=libffmpeg.a",

[bcf, 2017/03/01 23:59:20]

This shouldn't be necessary since we're not using "-Wl,--export-dynamic"
anymore.

[wzhong, 2017/03/02 00:12:40]

Not really. I believe in this case, without this, symbols will be visibility and
merged at runtime. We don't want them to merge.

[bcf, 2017/03/02 02:59:26]

So you're saying we still need this?

I thought the original purpose cause of this was '-Wl,--export-dynamic' being
added. This CL takes that away.

[wzhong, 2017/03/02 15:53:48]

Probably you're right.

The caveat is the symbols causing trouble here are written in assembly so please
verify on Chirp to see if multiple instances of ffmpeg work.

   ]
 
   if (!is_android) {
     ldflags += [
       # We want to statically link libstdc++/libgcc on Linux.
       # (On Android, libstdc++ and libgcc aren't used.)
       "-static-libstdc++",
       "-static-libgcc",
     ]
   }
@@ skipping 17 matching lines @@
   # libraries may still depend on them. Explicitly add the component library
   # directory to the rpath for the component build.
   if (is_component_build) {
     ldflags += [ "-Wl,-rpath=/system/chrome" ]
   }
 }
 
 config("executable_config") {
   configs = [ ":ldconfig" ]
 
-  if (current_cpu == "arm") {
+  if (!is_clang && current_cpu == "arm") {
     ldflags = [
       # Export stdlibc++ and libgcc symbols to force shlibs to refer to these
       # symbols from the executable.
       "-Wl,--export-dynamic",
 
       "-lm",  # stdlibc++ requires math.h
 
       # In case we redefined stdlibc++ symbols (e.g. tc_malloc)
       "-Wl,--allow-multiple-definition",
 
       "-Wl,--whole-archive",
       "-l:libstdc++.a",
       "-l:libgcc.a",
       "-Wl,--no-whole-archive",
     ]
 
     # Despite including libstdc++/libgcc archives, we still need to specify
     # static linking for them in order to prevent the executable from having a
     # dynamic dependency on them.
     configs += [ ":static_config" ]
   }
 }
 
 config("shared_library_config") {
   configs = [ ":ldconfig" ]
-  if (current_cpu == "arm") {
+  if (!is_clang && current_cpu == "arm") {
     configs += [ ":static_config" ]
   }
 }