aarch64: Treat void return as not passed in registers
aarch64: Treat void return as not passed in registers

This lets us do less post-processing when there's no return value.

Pan7/libffi,joshtriplett/libffi,Distrotech/libffi,bgarrels/libffi,s1341/libffi,biosbits/libffi,plicease/libffi,joshtriplett/libffi,nmav/libffi,rth7680/libffi,s1341/libffi,bgarrels/libffi,rth7680/libffi,s1341/libffi,plicease/libffi,Distrotech/libffi,Distrotech/libffi,plicease/libffi,Distrotech/libffi,bgarrels/libffi,biosbits/libffi,Pan7/libffi,nmav/libffi,bgarrels/libffi,rth7680/libffi,rth7680/libffi,nmav/libffi,joshtriplett/libffi,s1341/libffi,Pan7/libffi,nmav/libffi,Pan7/libffi,biosbits/libffi,plicease/libffi,joshtriplett/libffi,biosbits/libffi