[wasm] Only make needed regions writable

On Windows, the overhead of {SetPermissions} (which maps to a
{VirtualAlloc} call) heavily depends on the amount of memory on which
permissions are switched. Hence this CL changes permission switching
to only switch the code regions that are actually needed. This will
increase the number of system calls, but reduce the total size of
switched memory.

On a Unity benchmark, this reduced the lazy compilation time on Windows
from 13.7 seconds to 3.6 seconds (3.0 seconds without write protection).
On Linux, there is no measurable effect, but permission switching
generally seems to have way less overhead on Linux.

R=jkummerow@chromium.org

Bug: v8:11974
Change-Id: I46dd4ae9997587226b3d81166cf2e1128383ab34
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3077144


Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76163}