PR other/51165: add new adress_escapes predicate

[Aldy Hernandez]

As discussed in the PR, the problem here is that we are using 
ptr_deref_may_alias_global_p() to determine if a dereferenced address 
escapes, whereas we were previously using the now non existent 
is_call_clobbered.  The function ptr_deref_may_alias_global_p() does not 
understand SSA_NAMEs, whereas is_call_clobbered did.

Richi suggested using may_be_aliased() for DECLs.

The patch below abstracts an address_escapes_p() predicate for more 
generic use into the aliasing code.  Using this instead of 
ptr_deref_may_alias_global_p() fixes all 4 TM memory optimization 
regressions.  TM logging is now back in business.

Is this what you had in mind?  OK for trunk?
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