sim: add default cases to two switches in sim-options.c

This is the next compilation error I hit when I build all targets with
Clang:

    /home/simark/src/binutils-gdb/sim/aarch64/../common/sim-options.c:234:12: error: no case matching constant switch condition '0' [-Werror]                                                                    switch (WITH_ENVIRONMENT)
                      ^~~~~~~~~~~~~~~~                                                                                                                                                                 ./config.h:215:26: note: expanded from macro 'WITH_ENVIRONMENT'
    #define WITH_ENVIRONMENT ALL_ENVIRONMENT                                                                                                                                                                                    ^~~~~~~~~~~~~~~
    /home/simark/src/binutils-gdb/sim/aarch64/../common/sim-options.c:276:15: error: no case matching constant switch condition '0' [-Werror]                                                                switch (WITH_ALIGNMENT)
                  ^~~~~~~~~~~~~~                                                                                                                                                                       /home/simark/src/binutils-gdb/sim/aarch64/../common/sim-config.h:220:24: note: expanded from macro 'WITH_ALIGNMENT'
    #define WITH_ALIGNMENT 0
                           ^

This is a little bit special because these are switches on compile-time
value.  But regardless, the idea is that we logically can't reach the
switches if WITH_ENVIRONMENT == 0 or WITH_ALIGNMENT == 0, so the code is
correct.

In addition to getting rid of the compiler warning, adding default cases
to these switches ensure that if we do get in an unexpected situation,
it is caught.  In GDB, I'd use gdb_assert_not_reached, I don't know if
there is something similar in sim so I went with abort.

sim/common/ChangeLog:

	* sim-options.c (standard_option_handler): Add default cases to
	switches.

Change-Id: Ie237d67a201caa6b72de0d17cc815193417156b6