Both tests define a execute_native_thread_routine function that we
took from libstdc++. Unfortunately because of a bug this function
is not local in some versions of libstdc++ and so our similar named
function will clash when trying to link.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70476#c2
Simply rename our version to work around this.
Since we don't build this part of the test code for gcc >= 6, this
issue only happens if the buggy libstdc++ thread code is used together
with gcc 5. This is the case with for example devtoolset-4-gcc-5.
git-svn-id: svn://svn.valgrind.org/valgrind/trunk@15842
