Comment # 3 on bug 935510 from Richard Biener

ffi_prep_cif returns FFI_BAD_ABI, the caller passes FFI_DEFAULT_ABI (which
maps to FFI_SYSV on x86_64-linux).  This isn't in the range of the targets
FFI_FIRST_ABI to FFI_LAST_ABI (it maps to FFI_FIRST_ABI).

Ok, somehow the libffi4-gcc5-devel on Factory x86_64 ended up with a ffi.h
containing

/* Specify which architecture libffi is configured for. */
#ifndef X86
#define X86
#endif

(broken, should be X86_64)

Still investigating.