Testbench for Kotlin/Native EAP

The original pi.c was taken from http://bellard.org/pi/pi.c (added a plain loop to calculate digits from 1 to n instead of digits around n-th)

Computing 1000 decimal digits of π, average time on 20 runs:

C	6.8 sec
Kotlin/Native interop with C	6.8 sec
Kotlin/Native 0.7 EAP	6.9 sec
Kotlin/Native 0.6.2 EAP	9.3 sec
Kotlin/Native 0.6 EAP	10.2 sec
Kotlin/Native 0.4 EAP	11.4 sec

Result - performance in this test is almost identical, Kotlin is approx. 2% slower.

But it is EAP, so even that 2% may be fixed in next versions.