[AArch64] Update comment on GHC CC (llvm#72761)

Currently, there are a couple dead links in the comment surrounding the
tablegen implementtion of the GHC calling convention in AArch64. There
was some refactoring in GHC that moved things around. This patch fixes
up the comment to match the current state of the repository to make it
easier for future readers to reference the relevant documentation.

Author: boomanaiden154

llvm/lib/Target/AArch64/AArch64CallingConvention.td

@@ -333,7 +333,7 @@ def CC_AArch64_DarwinPCS_ILP32_VarArg : CallingConv<[
 // The only documentation is the GHC source code, specifically the C header
 // file:
 //
-//     https://github.com/ghc/ghc/blob/master/includes/stg/MachRegs.h
+//    https://github.com/ghc/ghc/blob/master/rts/include/stg/MachRegs.h
 //
 // which defines the registers for the Spineless Tagless G-Machine (STG) that
 // GHC uses to implement lazy evaluation. The generic STG machine has a set of
@@ -344,8 +344,10 @@ def CC_AArch64_DarwinPCS_ILP32_VarArg : CallingConv<[
 //
 //    https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/GeneratedCode
 //
-// The AArch64 register mapping is under the heading "The ARMv8/AArch64 ABI
-// register mapping".
+// The AArch64 register mapping is defined in the following header file:
+//
+//    https://github.com/ghc/ghc/blob/master/rts/include/stg/MachRegs/arm64.h
+//
 
 let Entry = 1 in
 def CC_AArch64_GHC : CallingConv<[