handling fun exit node

[jumormt]

1. isNotRetFunction -> hasReturn
2. do not connect exit to return site for no return function
3. connect all unreachable to fun exit for no return function

[codecov]

Codecov Report

Merging #1266 (eb766db) into master (ccbff5c) will increase coverage by 0.00%.
Report is 1 commits behind head on master.
The diff coverage is 100.00%.

❗ Current head eb766db differs from pull request most recent head ee9e6ce. Consider uploading reports for the commit ee9e6ce to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1266   +/-   ##
=======================================
  Coverage   64.51%   64.51%           
=======================================
  Files         223      223           
  Lines       23781    23785    +4     
=======================================
+ Hits        15342    15346    +4     
  Misses       8439     8439           

Files	Coverage Δ
svf-llvm/lib/ICFGBuilder.cpp	98.92% <100.00%> (+0.04%)	⬆️
svf/include/SVFIR/SVFValue.h	89.04% <100.00%> (ø)
svf/lib/Graphs/ICFG.cpp	71.09% <100.00%> (ø)
svf/lib/MSSA/MemSSA.cpp	73.55% <100.00%> (ø)