openssl: include OpenSSL headers only when we're buliding against it

We need to include the initialisation and construction functions in all
backend, so we include this header when building against SecureTransport
and WinHTTP as well.

src/openssl_stream.h

@@ -7,11 +7,6 @@
 #ifndef INCLUDE_openssl_stream_h__
 #define INCLUDE_openssl_stream_h__
 
-#include <openssl/ssl.h>
-#include <openssl/err.h>
-#include <openssl/x509v3.h>
-#include <openssl/bio.h>
-
 #include "git2/sys/stream.h"
 
 extern int git_openssl_stream_global_init(void);
@@ -24,6 +19,14 @@ extern int git_openssl_stream_new(git_stream **out, const char *host, const char
  * we can program against the interface instead of littering the implementation
  * with ifdefs.
  */
+#ifdef GIT_OPENSSL
+# include <openssl/ssl.h>
+# include <openssl/err.h>
+# include <openssl/x509v3.h>
+# include <openssl/bio.h>
+
+
+
 # if OPENSSL_VERSION_NUMBER < 0x10100000L
 
 GIT_INLINE(BIO_METHOD*) BIO_meth_new(int type, const char *name)
@@ -113,6 +116,7 @@ GIT_INLINE(const unsigned char *) ASN1_STRING_get0_data(const ASN1_STRING *x)
 	return ASN1_STRING_data((ASN1_STRING *)x);
 }
 
-# endif
+# endif // OpenSSL < 1.1
+#endif // GIT_OPENSSL
 
 #endif