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/configure

@@ -602,8 +602,6 @@ PATH_SEPARATOR
 SHELL
 WERROR_CFLAGS
 WARN_CFLAGS
-sim_xor_endian
-sim_smp
 sim_reserved_bits
 sim_inline
 sim_hw
@@ -614,9 +612,7 @@ sim_scache
 sim_float
 sim_endian
 sim_bitsize
-sim_assert
-sim_alignment
-sim_environment'
+sim_alignment'
 ac_subst_files=''
 ac_user_opts='
 enable_option_checking