Removes unnecessary includes of v8.h from
src/diagnostics/gdb-jit.h
src/diagnostics/system-jit-win.h
src/diagnostics/unwinder.h

by predeclaring types or using more appropriate headers.

Bug: v8:11879
Change-Id: I17f42acfef8e61133988453d67c3c0d473ff0337
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3045702
Auto-Submit: Dan Elphick <delphick@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75870}