New gpg-error.m4 detects gpgrt-config, too.
And configure supplies --libdir when it invokes gpgrt-config.
For other *.m4 (libassuan, ksba, libgcrypt, ntbtls), it is possible for them to check GPGRT_CONFIG to use gpgrt-config if any.
For npth.m4, it can do that too, with no hard dependency to libgpg-error.

A bit tricky, but this would be good to use gpgrt-config by gpg-error.m4.
I say "tricky", because its name is gpg-error.m4 but it configure GPGRT_CONFIG to access to GPG_ERROR_CONFIG.

It might be good idea to provide libgcrypt.pc in libgcrypt 1.8.x for forward compatibility with libgpg-error 1.33.

Well, I changed my mind. Use of new gpgrt-config requires software update to introduce gpgrt.m4 and update of configure.ac to switch gpgrt from gpg-error, in standard way.
That's too much this time. It's good to defer this change.

OK, I'll change to use gpgrt-config, along with requiring newer version of libgpg-error.

May I suggest to use a (new) gpgrt-config instead of the current name libgpg-error-config. The long term plan is to change the name of the library.

This is the dependency graph:

Done for gpgme.

Done for npth.

Thanks for the report.
Fixed in master.

Add the tag of npth (forgotten).

Done for libassuan

Thanks for the list

Here is the list:

• libgcrypt
• libassuan
• ntbtls
• gpgme : autogen.sh is ready
• npth

ntbtls 0.1.2 has been released as well gnupg 2.2.1 with other fixes and the Windows installer using that new ntbtls.

I added the missing curves to ntbtls and will soon do a new release. To please some folks here I also added the Brainpool curves ;-)

You can't access that server even from Windows7 due to an uncommon ECC curve. I need to investigate but it is likely that ntbtls does not yet support it.