Fix linkcheck (#1398)

* Don't linkcheck stackoverflow.com, it's rate limited and times out

* Fix XZ link post-backdoor

conf.py

@@ -105,8 +105,10 @@
     r'https://github.com/python/bedevere/#pr-state-machine',
     # "Anchor not found":
     r'https://packaging.python.org/.*#',
+    # "-rate limited-", causing a timeout
+    r'https://stackoverflow.com/.*',
     # Discord doesn't allow robot crawlers: "403 Client Error: Forbidden"
-    r'https://support.discord.com/hc/en-us/articles/219070107-Server-Nicknames',
+    'https://support.discord.com/hc/en-us/articles/219070107-Server-Nicknames',
 ]
 
 rediraffe_redirects = {

getting-started/setup-building.rst

@@ -779,7 +779,7 @@ on Linux, macOS and iOS.
 
    As with CPython itself, the dependencies for CPython must be compiled for
    each of the hardware architectures that iOS supports. Consult the
-   documentation for `XZ <https://xz.tukaani.org/xz-utils/>`__, `bzip2
+   documentation for `XZ <https://tukaani.org/xz/>`__, `bzip2
    <https://sourceware.org/bzip2/>`__, `OpenSSL <https://www.openssl.org>`__ and
    `libffi <https://github.com/libffi/libffi>`__ for details on how to configure
    the project for cross-platform iOS builds.