app-misc/gcstar: Restore ${ED} to install's prefix argument, otherwise gcstar fails...

app-misc/gcstar: Restore ${ED} to install's prefix argument, otherwise gcstar fails to install with access violations (see bug #139940, comment 15). Gcstar's install lacks any concept of DESTDIR; to install it to ${ED} with a prefix of /usr, we need to use --prefix="${ED}usr". Note that using prefix-aware variables is safe because gcstar loads everything relative to the main executable's path.

svn path=/sunrise/; revision=12172