ntdll: Add a __chkstk entry point for x86_64.

dlls/kernel32/kernel32.spec

@@ -1277,6 +1277,8 @@
 @ stdcall WriteProfileStringW(wstr wstr wstr)
 @ stdcall WriteTapemark(ptr long long long)
 @ stdcall ZombifyActCtx(ptr)
+@ stdcall -arch=x86_64 -private __C_specific_handler(ptr long ptr ptr) ntdll.__C_specific_handler
+@ stdcall -arch=x86_64 -private -norelay __chkstk() ntdll.__chkstk
 @ stub _DebugOut
 @ stub _DebugPrintf
 @ stdcall _hread(long ptr long)

dlls/ntdll/ntdll.spec

@@ -1244,6 +1244,7 @@
 # @ stub _CIsin
 # @ stub _CIsqrt
 @ stdcall -arch=x86_64 __C_specific_handler(ptr long ptr ptr)
+@ stdcall -private -arch=x86_64 -norelay __chkstk()
 # @ stub __isascii
 # @ stub __iscsym
 # @ stub __iscsymf

dlls/ntdll/signal_x86_64.c

@@ -1483,6 +1483,14 @@ static void restore_context( const CONTEXT *context, ucontext_t *sigcontext )
 }
 
 
+/**************************************************************************
+ *		__chkstk (NTDLL.@)
+ *
+ * Supposed to touch all the stack pages, but we shouldn't need that.
+ */
+__ASM_GLOBAL_FUNC( __chkstk, "ret" );
+
+
 /***********************************************************************
  *		RtlCaptureContext (NTDLL.@)
  */