demote -fsanitize=pointer-overflow to warning

Clang 10 added a new check we and libjpeg-turbo fail.
We need to investigate these failures, but I don't
want that to stop us rolling clang_win.

Bug: skia:9731
Change-Id: Ifdbb16ea0e2bacd30547d4a82a839563a9496d9f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/260948
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>

Author: Mike Klein

gn/BUILD.gn

@@ -277,6 +277,13 @@ config("default") {
       "-fno-sanitize-recover=$sanitizers",
       "-fsanitize-blacklist=$_blacklist",
     ]
+
+    # TODO(mtklein): we need to fix "nullptr + k" issues
+    # where k != 0 in C++, or in C, k == anything at all.
+    # We have failures in Skia and libjpeg-turbo, at least.
+    # See skia:9731.
+    cflags += [ "-fsanitize-recover=pointer-overflow" ]
+
     ldflags += [ "-fsanitize=$sanitizers" ]
 
     if (is_win) {