Do not include gcrypt.h for newer GnuTLS versions

Not linking against Libgcrypt is not enough, we also should not try to
include headers. This fixes GnuTLS >= 2.12 detection when Libgcrypt
headers are not installed/found.

src/configure

@@ -99,13 +99,15 @@ GNUTLS_INCLUDE="$(pkg-config gnutls --cflags 2>& 5 || true)"
 GNUTLS_LIBS="$(pkg-config gnutls --libs 2>& 5 || true) -lgnutls-openssl"
 
 # GnuTLS >= 2.12 does not need explicit gcrypt linking anymore
+gcrypt_h=""
 if $(pkg-config --max-version=2.11.99 gnutls 2>& 5 || false); then
 	GNUTLS_LIBS="$GNUTLS_LIBS -lgcrypt"
+	gcrypt_h="#include <gcrypt.h>"
 fi
 
 cat << EOF > test.c
 #include <gnutls/openssl.h>
-#include <gcrypt.h>
+$gcrypt_h
 #include <errno.h>
 
 int main()

src/mail.c

@@ -46,12 +46,13 @@
 
 #if defined(HAVE_GNUTLS)
 #include <gnutls/openssl.h>
-#include <gcrypt.h>
+
 #define MD5Init		MD5_Init
 #define MD5Update	MD5_Update
 #define MD5Final	MD5_Final
 
 #if GNUTLS_VERSION_NUMBER <= 0x020b00
+#include <gcrypt.h>
 /* gcrypt mutex setup is only needed for GnuTLS < 2.12 */
 
 static int gk_gcry_glib_mutex_init (void **priv) {