package/mariadb: use host-openssl from buildroot-system

package/mariadb: use host-openssl from buildroot-system

mariadb no longer allows the WITH_SSL=OFF configure option. It will
instead search for openssl or gnutls headers, and if missing error out
with:

  CMake Error at /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:137 (message):
    Could NOT find GnuTLS (missing: GNUTLS_LIBRARY GNUTLS_INCLUDE_DIR)
    (Required is at least version "3.3.24")
  Call Stack (most recent call first):
    /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:378 (_FPHSA_FAILURE_MESSAGE)
    /usr/share/cmake/Modules/FindGnuTLS.cmake:54 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
    libmariadb/CMakeLists.txt:298 (FIND_PACKAGE)

Therefore, make host-mariadb depend on host-openssl, and tell mariadb
to use the system openssl.

This was not found by autobuilders because mariadb isn't built in the
autobuilders (it's part of a choice).

Note that the target mariadb already has an unconditional dependency
on openssl.

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Tested-by: Ryan Coe <bluemrp9@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>