[Bug libstdc++/69310] [6 Regression] Revision r232454 breaks bootstrap on x86_64-apple-darwin15

[howarth.at.gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69310

--- Comment #10 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
It is unclear if the changes in r232454, to avoid the explicit linkage on
libitm, can ever be made darwin-friendly. On darwin, every single executable
linked against libstdc++ would require -Wl,-undefined,dynamic_lookup on the
linkage to avoid linkage errors from the undefined symbols from libitm within
libstdc++.