Support $! stringification of socket error codes on Windows.

The winsock error codes from WSAGetLastError() are stored by
Perl in errno, and there is some code in win32_strerror() that
would stringify them, but that code is never called when Perl
is built with the default WIN32IO_IS_STDIO setting.

This patch enables the win32_strerror() override unconditionally
and also fixes a potential memory corruption issue by using
the FORMAT_MESSAGE_IGNORE_INSERTS flag to ignore any parameter
substitution codes that may be embedded in the error message.

This now works as expected:

C:\git\perl>perl -Ilib -MPOSIX -E "$!=POSIX::EWOULDBLOCK; say $!"
A non-blocking socket operation could not be completed immediately.

1 files changed, 8 insertions, 6 deletions

diff --git a/win32/win32.c b/win32/win32.c
index 0302836ea7..050c50cfec 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -64,7 +64,6 @@ typedef struct {
 #define PERL_NO_GET_CONTEXT
 #include "XSUB.h"
 
-#include "Win32iop.h"
 #include <fcntl.h>
 #ifndef __GNUC__
 /* assert.h conflicts with #define of assert in perl.h */
@@ -2623,21 +2622,24 @@ win32_strerror(int e)
 #if !defined __BORLANDC__ && !defined __MINGW32__      /* compiler intolerance */
     extern int sys_nerr;
 #endif
-    DWORD source = 0;
 
     if (e < 0 || e > sys_nerr) {
         dTHX;
 	if (e < 0)
 	    e = GetLastError();
 
-	if (FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, &source, e, 0,
-			  w32_strerror_buffer,
-			  sizeof(w32_strerror_buffer), NULL) == 0)
+	if (FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM
+                         |FORMAT_MESSAGE_IGNORE_INSERTS, NULL, e, 0,
+			  w32_strerror_buffer, sizeof(w32_strerror_buffer),
+                          NULL) == 0)
+        {
 	    strcpy(w32_strerror_buffer, "Unknown Error");
-
+        }
 	return w32_strerror_buffer;
     }
+#undef strerror
     return strerror(e);
+#define strerror win32_strerror
 }
 
 DllExport void