win32: add missing AttachConsole export to kernel32.def

AttachConsole has been exported from kernel32.dll since Windows XP
but was absent from TCC's import definitions, causing
"undefined symbol 'AttachConsole'" at link time for code that uses it.

Author: H-language

win32/lib/kernel32.def

@@ -9,6 +9,7 @@ AllocConsole
 AllocLSCallback
 AllocSLCallback
 AreFileApisANSI
+AttachConsole
 BackupRead
 BackupSeek
 BackupWrite