This CL uses pc-relative jumps and calls (B/BL) for calls from embedded
builtins to embedded builtins. To make this work, the code range size is
limited to 32MB on arm during mksnapshot, which ensures that all builtin
to builtin offsets for jumps/calls fit into the B/BL immediate. At code
generation time, we put a placeholder into the instruction offset which
we resolve to the right code object when the code is copied to the heap.
We use a new relocation mode RELATIVE_CODE_TARGET for these relative jumps.
The relocation mode RELATIVE_CODE_TARGET should never appear after
generating the snapshot.

We modify the target_address/set_target_address methods of RelocInfo
such that they return the absolute target addresses for pc-relative B/BL
instructions. This ensures that the GC can treat RELATIVE_CODE_TARGET in
the same way as code targets. This, however, only matters during
snapshot creation time, and production code never contains
RELATIVE_CODE_TARGET relocations.

Bug: v8:6666
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: If7eab83ad588859ca87c654a5ddc3e37caea884c
Reviewed-on: https://chromium-review.googlesource.com/1117181Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54320}