Deb: switch from usr/include/mysql to usr/include/mariadb

Matching libmariadb-dev package contents in official Debian repositories,
the MariaDB Connector/C files should go into a folder using the 'mariadb'
name. For compatibility with sources that expect to find 'mysql' stuff,
create a symlink from include/mysql to include/mariadb.

cmake/install_layout.cmake

@@ -176,7 +176,7 @@ SET(INSTALL_SYSCONF2DIR_DEB             "/etc/mysql/conf.d")
 SET(INSTALL_LIBDIR_DEB                  "lib")
 SET(INSTALL_PLUGINDIR_DEB               "lib/mysql/plugin")
 #
-SET(INSTALL_INCLUDEDIR_DEB              "include/mysql")
+SET(INSTALL_INCLUDEDIR_DEB              "include/mariadb")
 #
 SET(INSTALL_DOCDIR_DEB                  "share/doc")
 SET(INSTALL_DOCREADMEDIR_DEB            "share/doc")

debian/libmariadb-dev-compat.links

 usr/bin/mariadb_config usr/bin/mysql_config
+usr/include/mariadb usr/include/mysql
 usr/share/pkgconfig/mariadb.pc usr/share/pkgconfig/mysqlclient.pc

debian/libmariadb-dev.install

 usr/bin/mariadb_config
-usr/include/mysql
+usr/include/mariadb
 usr/lib/*/libmariadb.so
 usr/lib/*/libmariadbclient.so
 usr/lib/*/libmariadbclient.a

debian/libmariadb-dev.links

-usr/include/mysql usr/include/mariadb
 usr/share/man/man1/mysql_config.1.gz usr/share/man/man1/mariadb_config.1.gz