[PATCH] tests: Fix undefined reference to 'pthread_create'

[NIIBE Yutaka]

Hello,

I think I located the cause.  It is a bug in m4/gpg-error.m4 (from
libgpg-error).  I'm going to push a fix to master (of libgcrypt).  Then,
I'll fix libgpg-error.

Clemens Lang wrote:
> I think the problem here is that this used libgpg-error 1.31, which does not ship a pkgconfig file.
>
> What is the minimum version of libgpg-error required by libgcrypt?

It is 1.27.  It doesn't provide gpg-error.pc, but it supports
gpg-error-config script.

(Unified config script gpgrt-config and gpg-error.pc is since version
1.33.)

libgpg-error 1.27 has old version of gpgrt-config, which is not unified
version.  This older gpgrt-config confuses the m4 script of
m4/gpg-error.m4.
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