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

[NIIBE Yutaka]

Hello,

Thank you for your report.

Clemens Lang wrote:
> * configure.ac (HAVE_PTHREAD): Expose as AM_CONDITIONAL for use in
>   Makefile.am
> * tests/Makefile.am: Link against pthread for tests that use it
>
> --
>
> Compilation on CentOS 8 Stream failed without this.

Could you please show us the build log (on that OS) for libgpg-error?

When -lpthread is needed, GPG_ERROR_MT_LIBS should have that.
(Or else, it may also fail in other places like compiling GnuPG.)

For the build, libgcrypt depends on gpg-error.pc of libgpg-error, and
uses GPG_ERROR_MT_CFLAGS and GPG_ERROR_MT_LIBS.  It is generated by the
build of libgpg-error using Gnulib's M4 script m4/threadlib.m4.

If something goes wrong, we need to fix libgpg-error.
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