If GPerfTools and/or the SYSTEM_SQLITE options are enabled, the test
suite fails to build (GPerfTools is not linked explicitly in CMakeLists.txt,
but becomes required by SimGear, so the linker failes with an "undefined
reference" error; the SQLite library the test suite links against is always
hardcoded to the FG-provided one).
This patch adds the GPerfTools library to the target link libraries
(if the profiler is enabled) and links to the system SQLite library
whenever SYSTEM_SQLITE is enabled.
Compile a useful subset of FG as a shared library, and add two basic
uses of this to exercise some Flightplan / RoutePath / navaid
functions.
The test framework can/will be expanded incrementally from here, this
is just a starting point.
