Fix args parsing

[cpunion]

• extract common cmd flags, for better cmd args parse
  • E.g. currently llgo build -v -o xxx failed

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.41%. Comparing base (a257b7b) to head (ebc0234).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1067   +/-   ##
=======================================
  Coverage   80.41%   80.41%           
=======================================
  Files          45       45           
  Lines        7921     7921           
=======================================
  Hits         6370     6370           
  Misses       1479     1479           
  Partials       72       72           

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