Avoid creating super long variable names for unconstrained read.
Avoid creating super long variable names for unconstrained read.

When there are many variables used in one AST, the variable name of that
AST might become extremely long. This issue may create excessive memory
pressure during symbolic execution or even CFG recovery (using
CFGAccurate).

This issue is reported by user @ange (Angelos Oikonomopoulos) on angr
Slack channel. Thanks @ange for reporting this issue and providing a
minimal test case.

Signed-off-by: Fish <64875fcccaac069fcb3e0e201e7d5b9166641608@cs.ucsb.edu>

f-prettyland/angr,f-prettyland/angr,tyb0807/angr,iamahuman/angr,chubbymaggie/angr,f-prettyland/angr,angr/angr,schieb/angr,tyb0807/angr,axt/angr,angr/angr,iamahuman/angr,angr/angr,tyb0807/angr,axt/angr,axt/angr,chubbymaggie/angr,chubbymaggie/angr,iamahuman/angr,schieb/angr,angr/simuvex,schieb/angr