verilog_defaults - set default options for read_verilog#

yosys> help verilog_defaults#
verilog_defaults -add [options]
Add the specified options to the list of default options to read_verilog.
verilog_defaults -clear
Clear the list of Verilog default options.
verilog_defaults -push
verilog_defaults -pop
Push or pop the list of default options to a stack. Note that -push does
not imply -clear.