Mark macros.error as .noreturn. (#23081)

Closes #14329 

Marks `macros.error` as `.noreturn` so that it can be used in
expressions. This also fixes the issue that occurred in #19659 where a
stmt that could be an expression (Due to having `discardable` procs at
the end of other branches) would believe a `noreturn` proc is returning
the same type e.g.
```nim
 proc bar(): int {.discardable.} = discard

if true: bar()
else: quit(0) # Says that quit is of type `int` and needs to be used/discarded except it actually has no return type
```

lib/core/macros.nim

@@ -427,7 +427,12 @@ proc copyNimTree*(n: NimNode): NimNode {.magic: "NCopyNimTree", noSideEffect.} =
       let x = 12
       echo x
 
-proc error*(msg: string, n: NimNode = nil) {.magic: "NError", benign.}
+when defined(nimHasNoReturnError):
+  {.pragma: errorNoReturn, noreturn.}
+else:
+  {.pragma: errorNoReturn.}
+
+proc error*(msg: string, n: NimNode = nil) {.magic: "NError", benign, errorNoReturn.}
   ## Writes an error message at compile time. The optional `n: NimNode`
   ## parameter is used as the source for file and line number information in
   ## the compilation error message.