The BFD linker requires the `COMMONPAGESIZE` emulation parameter to be
set in order to enable RELRO support for AArch64. As we are adding a
custom `emulparams` file anyways, let's also tell LD that our ELF
interpreter is called `/usr/lib/Loader.so`.
This commit also removes some vestigial references to i686 SerenityOS.
The one in `gas/configure.tgt` is still needed, as it also handles
x86_64.
