As the fix for 4415774, we need to detect if glibc is running in floating
stack mode (i686) or if it's running in old 2M fixed-stack mode (i386).
The detection is done by checking if glibc has the new API pthread_getattr_np().

However, many recent Linux distributions with latest glibc release are
still running in fixed stack mode, since pthread_getattr_np() is present
in glibc since 2.2.3, this can cause VM to believe incorrectly it is running
on floating stack. It may have some performance impact (because
pthread_getspecific implementation is slow on fixed stack pthread) as
well as making some of the logic look confusing.