[SV 63537] Pass enabled-by-default switches to submake

[SV 63537] Pass enabled-by-default switches to submake

Certain switches, such as -S or --no-silent, turn on behavior that is
enabled by default.  When a switch is specified via the command line,
makefile, or env, ensure the switch is added to MAKEFLAGS.

* src/main.c (struct command_switch): Add bit "specified".
(switches): Initialize command_switch->specified.
(decode_switches): Set command_switch->specified.
(define_makeflags): Check command_switch->specified.