sim: move many common settings from CPPFLAGS to config.h

Rather than stuffing the command line with a bunch of -D flags, start
moving things to config.h which is managed by autoheader.  This makes
the makefile a bit simpler and the build output tighter, and it makes
the migration to automake easier as there are fewer vars to juggle.

We'll want to move the other options out too, but it'll take more work.

sim/common/sim-options.c

@@ -119,14 +119,12 @@ static const OPTION standard_options[] =
       'E', "big|little", "Set endianness",
       standard_option_handler, NULL },
 
-#ifdef SIM_HAVE_ENVIRONMENT
   /* This option isn't supported unless all choices are supported in keeping
      with the goal of not printing in --help output things the simulator can't
      do [as opposed to things that just haven't been configured in].  */
   { {"environment", required_argument, NULL, OPTION_ENVIRONMENT},
       '\0', "user|virtual|operating", "Set running environment",
       standard_option_handler },
-#endif
 
   { {"alignment", required_argument, NULL, OPTION_ALIGNMENT},
       '\0', "strict|nonstrict|forced", "Set memory access alignment",