arm64: pass code model to LLVMgold

With LTO_CLANG, even if we pass -mcmodel to clang, the flag isn't
stored in the generated LLVM IR, which means it won't be used for
the actual compilation at link time. Therefore, the flag needs to
be passed to LLVMgold to actually take effect.

Bug: 62093296
Bug: 67506682
Change-Id: I5cd21f97c800466f1bce039df56101ce4087ae20
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>