Clang on ARM64 places the .rodata section into the same segment
as .text. On RHEL 8 ARM64, the kernel is configured for 64kB
memory pages. When we flip the page protection of the page containing
the GS cookie to RW and back to RO, we assume that the cookie lives
in a non-executable memory. This assumption is broken on RHEL 8 and
we end up setting protection of a part of the coreclr code to read
only instead of back to RX.

This change switches the linker we use to lld from the previously
used gnu linker. That linker places .rodata into a different segment
than .text by default. Moreover, I was planning to move to using
lld anyways to use all build tools from LLVM.

The lld linker has revealed that we were using absolute addresses in some
asm helpers and so load time relocation was necessary. This change fixes
it by replacing all of those by PC relative ones.

Use new images that have lld linker

There is no support for lld on that platform yet

Also update PGO stuff to not to use gold linker when
lld is present.