[Chromecast] GN - Only apply linker flags for arm

BUG= internal b/25566835

Review URL: https://codereview.chromium.org/1510973005

Cr-Commit-Position: refs/heads/master@{#364489}

build/config/chromecast/BUILD.gn

@@ -15,6 +15,7 @@ config("static_config") {
 }
 
 config("executable_config") {
+  if (current_cpu == "arm") {
     ldflags = [
       # Export stdlibc++ and libgcc symbols to force shlibs to refer to these
       # symbols from the executable.
@@ -35,8 +36,11 @@ config("executable_config") {
     # static linking for them in order to prevent the executable from having a
     # dynamic dependency on them.
     configs = [ ":static_config" ]
+  }
 }
 
 config("shared_library_config") {
+  if (current_cpu == "arm") {
     configs = [ ":static_config" ]
+  }
 }