arm64: executor: support data relocations in SyzOS

[ramosian-glider]

Right now SyzOS code cannot reference global variables from .data or .bss, it also gets broken if the compiler decides to play some clever tricks like creating a jump table or memcpy()ing a struct initializer from .rodata.

Because we cannot possibly make the compiler emit the guest-relevant data into a separate section, fixing this problem will require mapping all data sections into the guest address space, and fixing all the relocations. Alternatively, we can try to keep SyzOS relocation-free by scanning the code for ADRP instructions and reporting errors.

[ramosian-glider]

This strikes back on x86 now, and one can't simply scan x86 code for a particular instruction without pulling a disassembler into every reproducer out there.
I am planning to add a build-time validation script that will help detect at least some of the problems with x86 relocations.