link failure when building against latest libgcrypt

[Jim Meyering]

Hi,

Just a quick FYI that building gnupg (latest from git),
using the latest sources of libgcrypt leads to link failures like this:

    /w/gnupg/g10/mainproc.c:712: undefined reference to `gcry_md_start_debug'
    /w/gnupg/g10/mainproc.c:714: undefined reference to `gcry_md_start_debug'
    mainproc.o: In function `proc_tree':
    ...

That's due to this commit in libgcrypt:

    commit 889a25ed3333d1d7657b4b59ae21f6e8458f9027
    Author: Werner Koch <wk at gnupg.org>
    Date:   Thu Sep 15 18:24:23 2011 +0200

        Removed deprecated debug macros.

While I wait for gnupg to catch up, I worked around it
by adding this line to config.h:

  #define gcry_md_start_debug(a,b) /*empty */