Sort unwind list

Author: ehuss

src/items/external-blocks.md

@@ -159,13 +159,13 @@ r[items.extern.abi.efiapi]
 Like `"C"` and `"system"`, most platform-specific ABI strings also have a
 [corresponding `-unwind` variant][unwind-behavior]; specifically, these are:
 
+* `"aapcs-unwind"`
 * `"cdecl-unwind"`
-* `"stdcall-unwind"`
 * `"fastcall-unwind"`
+* `"stdcall-unwind"`
+* `"sysv64-unwind"`
 * `"thiscall-unwind"`
-* `"aapcs-unwind"`
 * `"win64-unwind"`
-* `"sysv64-unwind"`
 
 ## Variadic functions