re PR go/68496 ([libgo] reflect test fails on Linux x86-64)

re PR go/68496 ([libgo] reflect test fails on Linux x86-64)

	PR go/68496
    reflect: Allocate space for FFI functions returning a zero-sized type.

    The libffi library does not understand zero-sized types.  We represent
    them as a struct with a single field of type void.  If such a type is
    returned from a function, libffi will copy 1 byte of data.  Allocate
    space for that byte, although we won't use it.

    Fixes https://gcc.gnu.org/PR68496.

    Reviewed-on: https://go-review.googlesource.com/17175

From-SVN: r230776