https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87866
--- Comment #1 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
I backported a fix from the D sources so it should no longer segfault at least.
From what I can see, it should pick up the object.d source correctly.
-nostdinc -I /vol/gcc/src/hg/trunk/local/libphobos/libdruntime
Unless it really isn't in the -I path.
