Fix command line handling of warning flags.
Fix command line handling of warning flags.

Prevent an overflow of command line flags if the -Wall argument
is used multiple times, and fix processing of individual flags
that may be in the beginning of the warnings flag buffer.

themperek/iverilog,CastMi/iverilog,CastMi/iverilog,CastMi/iverilog,themperek/iverilog,themperek/iverilog