[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 #9 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
I suspect the current problem is from...

// Declare all libitm symbols we rely on, but make them weak so that we do
// not depend on libitm.

in libstdc++-v3/src/c++11/cow-stdexcept.cc. There needs to be an explicit
linkage on libitm to resolve these symbols for the build/genpreds executable.