package/civetweb: fix link failure due to missing OpenSSL dependency

package/civetweb: fix link failure due to missing OpenSSL dependency

During linking one OpenSSL dependecy is missing(-latomic) on linking
library list.

- Substitute explicit library list with `pkg-config libssl` when
  BR2_PACKAGE_OPENSSL is enabled. In such way all needed libraries
  will be included in linking list.

- Add also `host-pkgconf` to CIVETWEB_DEPENDENCIES if
  BR2_PACKAGE_OPENSSL is enabled to make it available for previous
  point.

Fixes:

  http://autobuild.buildroot.net/results/b2e210bdefe84f4ec9cfda79a33d81788fb7e66c/

Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>