litmus/herd: Compute test hashes the same way for litmus and herd.
Note: this commit and teh previous ones are consequences of the
merging of litmus and herd C parsers. Before litmus was getting rid
of toplevels '*' (C pointer type) of arguments, while herd was keeping it.
The merged parser keep the stars, while litmus strips them away just after
parsing. This complicate hash computation a bit.