[Bug sanitizer/89010] Update URLs in libsanitizer/README.gcc

[jg at jguk dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89010

--- Comment #3 from Jonny Grant <jg at jguk dot org> ---
(In reply to Martin Liška from comment #2)
> The patch looks fine to me. Will you send the patch to the GCC mailing list?

Sent!