Fix LiTL with recent libraries

[vlaforet]

Fixes: (First commit)

• gettid has been removed from src/utils.c as it is already defined in the C library
• pthread_yield has been renamed sched_yield

Second commit:
Fix the issue described in issue #11. pthread_create was not interposed and this resulted in contexts not being initialized.
The fix consists in linking to the new version of pthread_create with glibc >= 2.34. Backward compatibility is also assured by linking to the older version of pthread_create with glibc < 2.34.