mdbx: backport - ITS#8339 Solaris 10/11 robust mutex fixes.
mdbx: backport - ITS#8339 Solaris 10/11 robust mutex fixes.

Check for PTHREAD_MUTEX_ROBUST_NP definition (this doesn't work
on Linux/glibc because they used an enum). Zero out mutex before
initing.

Change-Id: Ic618a6a72fbd7680dd76d5fd0aef06545dcba994

leo-yuriev/libfpta,leo-yuriev/libfpta