Merge bitcoin/bitcoin#22516: macdeploy: alternative info to download the macOS SDK

f8f772d macdeploy: alternative info to download the macOS SDK (Antoine Poinsot)

Pull request description:

  The previous link wasn't accessible for me, this adds some instructions
  given to me by Hebasto on #bitcoin-core-builds as well as a shasum for
  the archive to quickly check the downloaded one is the right one before
  processing with the entire Guix build.

ACKs for top commit:
  fanquake:
    ACK f8f772d

Tree-SHA512: 620160b593ed8fa4ae4a748b8e72d67b93ff0ec9e6b8ef3c3ac5402c1c48ec0ac325a527b6278cdf84aaf51ba8194d4c366c412ffad141d0412add2710efcff5

Author: fanquake

contrib/macdeploy/README.md

@@ -16,7 +16,10 @@ Our current macOS SDK
 (`Xcode-12.1-12A7403-extracted-SDK-with-libcxx-headers.tar.gz`) can be
 extracted from
 [Xcode_12.1.xip](https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip).
-An Apple ID is needed to download this.
+Alternatively, after logging in to your account go to 'Downloads', then 'More'
+and look for [`Xcode_12.1`](https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip).
+An Apple ID and cookies enabled for the hostname are needed to download this.
+The `sha256sum` of the archive should be `612443b1894b39368a596ea1607f30cbb0481ad44d5e29c75edb71a6d2cf050f`.
 
 After Xcode version 7.x, Apple started shipping the `Xcode.app` in a `.xip`
 archive. This makes the SDK less-trivial to extract on non-macOS machines. One
@@ -76,7 +79,7 @@ and its `libLTO.so` rather than those from `llvmgcc`, as it was originally done
 
 To complicate things further, all builds must target an Apple SDK. These SDKs are free to
 download, but not redistributable. To obtain it, register for an Apple Developer Account,
-then download [Xcode_11.3.1](https://download.developer.apple.com/Developer_Tools/Xcode_11.3.1/Xcode_11.3.1.xip).
+then download [Xcode_12.1](https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip).
 
 This file is many gigabytes in size, but most (but not all) of what we need is
 contained only in a single directory: