added extended msg for failed library loads w/ incorrect DLL formats (#13950)

* added extended msg for failed library loads w/ incorrect DLL formats

* missing colon

* fix GetLastError()

* make GetLastError() available for windows console apps

* remove premature nullchar if outputting extra message

* if-protect nullchar detection

* better fix for message box code

lib/system/excpt.nim

@@ -17,13 +17,15 @@ var
     ## instead of `stdmsg.write` when printing stacktrace.
     ## Unstable API.
 
+when defined(windows):
+  proc GetLastError(): int32 {.header: "<windows.h>", nodecl.}
+  const ERROR_BAD_EXE_FORMAT = 193
+
 when not defined(windows) or not defined(guiapp):
   proc writeToStdErr(msg: cstring) = rawWrite(cstderr, msg)
-
 else:
   proc MessageBoxA(hWnd: pointer, lpText, lpCaption: cstring, uType: int): int32 {.
     header: "<windows.h>", nodecl.}
-
   proc writeToStdErr(msg: cstring) =
     discard MessageBoxA(nil, msg, nil, 0)