unix: Improve command line argument processing.

Per CPython everything which comes after the command, module or file
argument is not an option for the interpreter itself.  Hence the processing
of options should stop when encountering those, and the remainder be passed
as sys.argv.  Note the latter was already the case for a module or file but
not for a command.

This fixes issues like 'micropython myfile.py -h' showing the help and
exiting instead of passing '-h' as sys.argv[1], likewise for
'-X <something>' being treated as a special option no matter where it
occurs on the command line.

tests/cmdline/repl_inspect.py

@@ -1,2 +1,2 @@
-# cmdline: -c print("test") -i
+# cmdline: -i -c print("test")
 # -c option combined with -i option results in REPL

tests/cmdline/repl_inspect.py.exp

@@ -1,6 +1,6 @@
 test
 MicroPython \.\+ version
 Use \.\+
->>> # cmdline: -c print("test") -i
+>>> # cmdline: -i -c print("test")
 >>> # -c option combined with -i option results in REPL
 >>>