[Bug d/90893] ODR violation

[ibuclaw at gdcproject dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90893

--- Comment #1 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
libcall_type is internal to d/runtime.cc, so I'm fine with just prefixing it
with d_.