Disable pointer overflow checks.

These are leading to startup crashes in fuzzing builds. It can be
re-enabled once those are fixed or suppressed.

R=inferno@chromium.org

Change-Id: Ie5c8320bdabfd389fa514d71981f8d10dd6b174e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1978899
Auto-Submit: Martin Barbella <mbarbella@chromium.org>
Reviewed-by: Abhishek Arya <inferno@chromium.org>
Commit-Queue: Abhishek Arya <inferno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726914}

build/config/sanitizers/BUILD.gn

@@ -493,7 +493,6 @@ config("ubsan_flags") {
       "-fsanitize=integer-divide-by-zero",
       "-fsanitize=null",
       "-fsanitize=object-size",
-      "-fsanitize=pointer-overflow",
       "-fsanitize=return",
       "-fsanitize=returns-nonnull-attribute",
       "-fsanitize=shift-exponent",
@@ -536,7 +535,6 @@ config("ubsan_security_flags") {
     }
     cflags = [
       "-fsanitize=function",
-      "-fsanitize=pointer-overflow",
       "-fsanitize=shift",
       "-fsanitize=signed-integer-overflow",
       "-fsanitize=vla-bound",