libgcrypt: introduce mini variant

[jschwartzenberg]

Maintainer: @flyn-org
Compile tested: (mipsel_24kc_musl, TP-Link Archer C50v6, f10ee1e20966bdb86cb61a87338f953de1d86cc6)
Run tested: (mipsel_24kc_musl, TP-Link Archer C50v6, 24.10-rc2, tested a version compiled with the same flags still works with vpnc)

Description:
This allows building a smaller version of libgcrypt which takes up less disk space. This helps conserving space on devices with little flash while still providing a working libgcrypt.

Please let me know what you think of this PR! I intend to do more testing with the version built from this specific Makefile but my earlier tests shows that this works fine. Many thanks in advance for any feedback you might have!

[flyn-org]

I like the concept, but DES, MD5, and SHA1 are all obsolete. What led to your cipher/hash choices?

[jschwartzenberg]

I looked at what vpnc supports: https://github.com/streambinder/vpnc/blob/master/docs/about.md
I avoided anything that it doesn't support. I also had to add blake2 to avoid a build issue.

Possibly this is indeed a very specific set for my situation :)

Maybe it would be possible to experiment with different selections and observe the resulting sizes. I'm not really sure what would be the best approach.

[BKPepe]

This allows building a smaller version of libgcrypt which takes up less disk space.

May I know if you do have some numbers, so we can know how much is less? :) Thank you.

[jschwartzenberg]

This allows building a smaller version of libgcrypt which takes up less disk space.

May I know if you do have some numbers, so we can know how much is less? :) Thank you.

You might laugh, but here are the differences :)

800K ./build_dir/target-mipsel_24kc_musl/libgcrypt-1.10.3/ipkg-mipsel_24kc/libgcrypt/usr/lib/libgcrypt.so.20.4.3
584K ./build_dir/target-mipsel_24kc_musl/libgcrypt-mini/libgcrypt-1.10.3/.pkgdir/libgcrypt-mini/usr/lib/libgcrypt.so.20.4.3

On routers with tiny flash memory, this difference is enough to enable a few more small packages to be installed alongside :) :)