If needed, this will be done later via machdeps and not preprocessor macros

This reverts commit 1e6f9135.

It also changes pthread_t to match the usual definition on a glibc + Linux.

Prints the number of statements at which a garbled mix from a given origin
has been read and propagated, instead of the total number of times such a
garbled mix has been read/propagated.
This is more stable and depends less on states partitioning.

On assigns clause on struct, the message could be emitted even if no garbled
mix had been created, as the offsetmap for the struct was read as one cvalue,
which could be very imprecise.
Instead, this commit iters on the offsetmap and warn for each imprecise garbled
mix in the offsetmap, if any.