Embedded firebird is now version 3.0.

Supports MSVC 14.0.

Instead of fbembed, there are now two libraries: fbclient and
Engine12. fbclient is linked as fbembed before, Engine12 is loaded
at runtime from fbclient.

fb now needs system libtommath, which is supplied
as a new ExternalProject of LO.

Change-Id: I132939bdee745795b22f675e4265e9590079c45f
Reviewed-on: https://gerrit.libreoffice.org/27642Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Lionel Elie Mamane <lionel@mamane.lu>