Reland "Add -fsanitize=pointer-overflow to the UBSan config"

This is a reland of commit 103f0ee63afb8a42af04c9a152dc938e3571c128

The fix for leveldb is google/leveldb#1222,
but add a suppression for now.

Original change's description:
> Add -fsanitize=pointer-overflow to the UBSan config
>
> This required adding a couple suppressions for issues. Also fixing
> undefined behavior in BufferIteratorTest.ObjectSizeOverflow, which seems
> to have not been testing SIZE_MAX at all, and just when the buffer
> didn't have enough room.
>
> Bug: 40942951, 384391188, 385062729, 385155394
> Change-Id: If6defef3fbc4977632fccc63049901836d4a5347
> Cq-Include-Trybots: luci.chromium.try:linux_chromium_ubsan_rel_ng
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6108769
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Reviewed-by: Daniel Cheng <dcheng@chromium.org>
> Auto-Submit: David Benjamin <davidben@chromium.org>
> Commit-Queue: David Benjamin <davidben@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1399851}

Bug: 40942951, 384391188, 385062729, 385155394
Change-Id: I535d865661be49f11a291c62671557f7541b2bb9
Cq-Include-Trybots: luci.chromium.try:linux_chromium_ubsan_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6120908
Auto-Submit: David Benjamin <davidben@chromium.org>
Commit-Queue: David Benjamin <davidben@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1399949}
NOKEYCHECK=True
GitOrigin-RevId: fd7de0b84913bda60edcf21ab6c7c0cd017b1d70

Author: davidben

config/sanitizers/BUILD.gn

@@ -543,6 +543,7 @@ config("ubsan_flags") {
       "-fsanitize=null",
       "-fsanitize=nonnull-attribute",
       "-fsanitize=object-size",
+      "-fsanitize=pointer-overflow",
       "-fsanitize=return",
       "-fsanitize=returns-nonnull-attribute",
       "-fsanitize=shift",