[BOLT-AArch64] Support reordering spec06 gcc relocs

Summary:
Enhance the basic infrastructure for relocation mode for
AArch64 to make a reasonably large program work after reordering (gcc).

Detect jump table patterns and skip optimizing functions with jump
tables in AArch64, as those will require extra future effort to fully
decode. To make these work in relocation mode, we skip changing
the function body and introduce a mode to preserve even the original
nops. By not changing any local offsets in the function, the input
original jump tables should just work.

Functions with no jump tables are optimized with BB reordering. No other
optimizations have been tested.

(cherry picked from FBD6130117)