kdePackages.akonadi: restore mysql backend

I guess we're stuck with it for the time being.

pkgs/kde/gear/akonadi/default.nix

···
 {
+  lib,
   mkKdeDerivation,
   qttools,
   accounts-qt,
   kaccounts-integration,
   shared-mime-info,
   xz,
+  mariadb,
 }:
 mkKdeDerivation {
   pname = "akonadi";
 
-  # FIXME(later): investigate nixpkgs patches
+  patches = [
+    # Always regenerate MySQL config, as the store paths don't have accurate timestamps
+    ./ignore-mysql-config-timestamp.patch
+  ];
+
+  extraCmakeFlags = [
+    "-DMYSQLD_SCRIPTS_PATH=${lib.getBin mariadb}/bin"
+  ];
 
   extraNativeBuildInputs = [qttools shared-mime-info];
-  extraBuildInputs = [kaccounts-integration accounts-qt xz];
+  extraBuildInputs = [kaccounts-integration accounts-qt xz mariadb];
 }

pkgs/kde/gear/akonadi/ignore-mysql-config-timestamp.patch

···
+--- a/src/server/storage/dbconfigmysql.cpp
++++ b/src/server/storage/dbconfigmysql.cpp
+@@ -241,8 +241,7 @@ bool DbConfigMysql::startInternalServer()
+     bool confUpdate = false;
+     QFile actualFile(actualConfig);
+     // update conf only if either global (or local) is newer than actual
+-    if ((QFileInfo(globalConfig).lastModified() > QFileInfo(actualFile).lastModified())
+-        || (QFileInfo(localConfig).lastModified() > QFileInfo(actualFile).lastModified())) {
++    if (true) {
+         QFile globalFile(globalConfig);
+         QFile localFile(localConfig);
+         if (globalFile.open(QFile::ReadOnly) && actualFile.open(QFile::WriteOnly)) {