Align to the least common multiple of the large page size (known as a superpage or huge page) available on common platforms. Non-PAE x86 supports 4MB pages and x86-64 and arm64 support 2MB pages. FreeBSD automatically promotes large, superpage-aligned allocations, and this default image base address is consistent with GNU ld and gold.
Test updates are incomplete. I started with a sed replacement to update some of them, and am iterating through the remaining failures. Some tests need more investigation e.g. ELF/aarch64-prel32.s is producing a relocation out of range error.
Assuming there are no objections to this change in principle I will continue with the test updates.