mariadb-connector-c: fix static build

[SCOTT-HAMILTON]

Motivation for this change

Part of a bigger project to build Qt 5 statically #136107.

Things done

Fixed the build of pkgsStatic mariadb-connector-c_3_1 and mariadb-connector-c_3_2.

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 21.11 Release Notes (or backporting 21.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[veprbl]

@GrahamcOfBorg build pkgsStatic.mariadb-connector-c

[alyssais]

Looks fine to me, but I don't know anything about mariadb, so I won't merge for a little bit to give people who do a chance to way in and let us know if there are any pitfalls we might need to know about here.