Backporting "undefined reference to peg::enabler" fix to all versions older than 5.0.0; Fix tests to compile with clang 3.5.
Backporting "undefined reference to peg::enabler" fix to all versions older than 5.0.0; Fix tests to compile with clang 3.5.

Signed-off-by: Remigiusz Kołłątaj <2fbee66267fc98e13fb331b3267f5e191bcb467f@mobica.com>

yhirose/cpp-peglib