Update a broken link in documentation; NFC

This links to the same information but in a new location.

clang/include/clang/Basic/AttrDocs.td

@@ -2777,7 +2777,7 @@ On x86 targets, this attribute changes the calling convention to
 as possible in registers. It also tries to utilize registers for the
 return value whenever it is possible.
 
-.. _`__regcall`: https://software.intel.com/en-us/node/693069
+.. _`__regcall`: https://www.intel.com/content/www/us/en/docs/dpcpp-cpp-compiler/developer-guide-reference/2023-2/c-c-sycl-calling-conventions.html
   }];
 }