Merge pull request #876 from bradking/bcrypt-vs2010

Define bcrypt macro not available in Win 7 SDK
diff --git a/libarchive/archive_hmac.c b/libarchive/archive_hmac.c
index 1e0ae28..f299655 100644
--- a/libarchive/archive_hmac.c
+++ b/libarchive/archive_hmac.c
@@ -76,6 +76,10 @@
 
 #elif defined(_WIN32) && !defined(__CYGWIN__) && defined(HAVE_BCRYPT_H)
 
+#ifndef BCRYPT_HASH_REUSABLE_FLAG
+# define BCRYPT_HASH_REUSABLE_FLAG 0x00000020
+#endif
+
 static int
 __hmac_sha1_init(archive_hmac_sha1_ctx *ctx, const uint8_t *key, size_t key_len)
 {