tests/eina: make inclusion for define explicit and more compatible
Summary:
signal.h is not included with all build options somehow, making this
a bit unreliable. also check for define existence for random platforms
which don't define this symbol
Reviewers: devilhorns, ManMower
Reviewed By: ManMower
Subscribers: ManMower, cedric, committers
Tags: efl
Differential Revision: https://phab.enlightenment.org/D6535