Merge bitcoin/bitcoin#24955: guix: Improve error message about missed macOS SDK

914076e guix: Improve error message about missed macOS SDK (Hennadii Stepanov)

Pull request description:

  The error message now mentions another option for users to specify the path to the macOS SDK.

ACKs for top commit:
  fanquake:
    ACK 914076e

Tree-SHA512: e8b9a6c8aa984f02cdb4ad1eeb6c22510c0c74c47c831104ac410ef68b3bc40024a52400b5065a3e25603f8a040e72c8c464436cb9a0a018ca73b0d28e0d609d

Author: fanquake

contrib/guix/guix-build

@@ -132,7 +132,7 @@ for host in $HOSTS; do
                 echo "Found macOS SDK at '${OSX_SDK}', using..."
                 break
             else
-                echo "macOS SDK does not exist at '${OSX_SDK}', please place the extracted, untarred SDK there to perform darwin builds, exiting..."
+                echo "macOS SDK does not exist at '${OSX_SDK}', please place the extracted, untarred SDK there to perform darwin builds, or define SDK_PATH environment variable. Exiting..."
                 exit 1
             fi
             ;;