[Bug libstdc++/69386] [6 regression] r232586 breaks mingw-w64 bootstrap

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69386

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Hmm, those functions should not be extern "C". Could you please re-run that
compile command for eh_arm.cc with -save-temps and send me the preprocessed
source?

I'll start looking through the mingw-w64 headers for a cause.