The appropriate flag for HEASLR (--high-entropy-va) was added in
binutils 2.25.

Also set the image base >4GB so higher entropy gets applied to image
base randomization when used with HEASLR (8 -> 17 bits of
randomization).  Windows does this for compatibility because of "latent
pointer truncation issues".
Signed-off-by: Alex Smith <alex.smith@warpsharp.info>