another build failure on ppc64-linux

[Janis Johnson]

Bootstrap of current trunk on powerpc64-linux fails in libstdc++
building system_error.lo.  The code that fails was added a few days ago,
but the failure seems to be the same as the one reported in PR 31490.  I
verified that the patch from comment #10 of that PR allows bootstrap of
c,c++,fortran to succeed and now I'm doing a bootstrap and regtest of
all languages but Ada.  I'll report the results in the PR.

Janis