fix CFBBGbuilder bug

[jumormt]

do not connect return BB edge for no return function that does not have an exit BB

[codecov]

Codecov Report

Merging #1273 (d2c158b) into master (2b3b9f8) will increase coverage by 0.00%.
Report is 1 commits behind head on master.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1273   +/-   ##
=======================================
  Coverage   64.49%   64.49%           
=======================================
  Files         223      223           
  Lines       23800    23802    +2     
=======================================
+ Hits        15349    15351    +2     
  Misses       8451     8451           

Files	Coverage Δ
svf-llvm/lib/LLVMModule.cpp	82.77% <100.00%> (+0.03%)	⬆️
svf/include/SVFIR/SVFValue.h	88.81% <ø> (-0.23%)	⬇️
svf/lib/Graphs/ICFG.cpp	70.98% <100.00%> (-0.12%)	⬇️
svf/lib/SVFIR/SVFValue.cpp	74.77% <100.00%> (+1.18%)	⬆️

... and 1 file with indirect coverage changes