Run "make check". Test and verify TaggedSpiroCPsToBezier0() using pthreads

Libspiro does not use pthreads, but call-test makes use of it to check if
libspiro is able to handle multiple users and threads at the same time.
Phtread defaults limited to 380 threads unless changed to a higher value,
otherwise segfault (didn't test for pthread limit since #define=300).
If no pthreads is available, then do a sequential test instead, which is
good enough to verify libspiro returns valid info, but no multi-user check.

NOTE: Used "/100" to made different x,y coordinates for this test, maybe
it's due to fractional rounding of values, otherwise this test would fail
at above #define S_TESTS=4300 (something for a TODO future investigation).