[libsecret] build: Fix build without libgcrypt

[Stefan Walter <stefw src gnome org>]

commit 053ecbd8f70676c76cd0cfc5648256ccae27a1e8
Author: Stef Walter <stefw gnome org>
Date:   Wed Aug 8 07:57:09 2012 +0200

    build: Fix build without libgcrypt
    
     * Needed to use m4_ifdef on the libgcrypt autoconf macro
    
    https://bugzilla.gnome.org/show_bug.cgi?id=681330

 configure.ac |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 70295b8..138149e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -95,13 +95,19 @@ AC_ARG_ENABLE(gcrypt,
               ])
 
 if test "$enable_gcrypt" != "no"; then
-	AM_PATH_LIBGCRYPT($GCRYPT_LIBVER:$GCRYPT_VERSION,,
-	                  AC_MSG_ERROR([[
+
+	have_gcrypt="no"
+	m4_ifdef([AM_PATH_LIBGCRYPT],
+	         [AM_PATH_LIBGCRYPT($GCRYPT_LIBVER:$GCRYPT_VERSION, have_gcrypt=yes)])
+
+	if test $have_gcrypt != "yes"; then
+		AC_MSG_ERROR([[
 ***
 *** libgcrypt was not found. You may want to get it from
 *** ftp://ftp.gnupg.org/gcrypt/libgcrypt/
 ***
-	                  ]]))
+		]])
+	fi
 
 	AC_DEFINE(WITH_GCRYPT, 1, [Build with libgcypt and transport encryption])
 	AC_DEFINE_UNQUOTED(LIBGCRYPT_VERSION, "$GCRYPT_VERSION",