cmd/igop: update flag -mod -v -x -ssa -ssa-trace

[visualfc]

  -mod value
    	module download mode to use: readonly, vendor, or mod.
  -ssa
    	print SSA instruction code
  -ssa-trace
        trace SSA interpreter code
  -tags value
    	a comma-separated list of build tags to consider satisfied during the build
  -v	print the names of packages as they are compiled.
  -x	print the commands.