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

(Imported from upstream's daa96141d31dbe6a6fadc6afc7cf9d1284d9bdd8)

Change-Id: Ibc55db0909585c6472b92af519ffbe717b79c90c

crypto/sha/asm/sha512-x86_64.pl

diff --git a/crypto/sha/asm/sha512-x86_64.pl b/crypto/sha/asm/sha512-x86_64.pl
index 23456f0..5a7c5ac 100644
--- a/crypto/sha/asm/sha512-x86_64.pl
+++ b/crypto/sha/asm/sha512-x86_64.pl
@@ -2263,7 +2263,7 @@
 	ret
 .size	se_handler,.-se_handler
 ___
-$code.=<<___ if ($shaext);
+$code.=<<___ if ($SZ == 4 && $shaext);
 .type	shaext_handler,\@abi-omnipotent
 .align	16
 shaext_handler: