sha512-x86_64.pl: fix linking problem under Windows.

crypto/sha/asm/sha512-x86_64.pl

@@ -2262,7 +2262,9 @@ $code.=<<___;
 	pop	%rsi
 	ret
 .size	se_handler,.-se_handler
+___
 
+$code.=<<___ if ($SZ==4 && $shaext);
 .type	shaext_handler,\@abi-omnipotent
 .align	16
 shaext_handler:
@@ -2295,7 +2297,9 @@ shaext_handler:
 
 	jmp	.Lin_prologue
 .size	shaext_handler,.-shaext_handler
+___
 
+$code.=<<___;
 .section	.pdata
 .align	4
 	.rva	.LSEH_begin_$func