sim: common: split up acinclude.m4 into individual m4 files

This file is quite large and is getting unmanageable.  Split it apart
to follow aclocal best practices by putting one-macro-per-file.  There
shouldn't be any real functional changes here as can be seen in the
configure script regens.

sim/avr/configure

@@ -631,6 +631,14 @@ ac_includes_default="\
 
 ac_subst_vars='LTLIBOBJS
 LIBOBJS
+sim_reserved_bits
+sim_hw
+sim_hw_objs
+sim_hw_cflags
+sim_default_model
+sim_scache
+sim_float
+sim_bitsize
 cgen_breaks
 REPORT_BUGS_TEXI
 REPORT_BUGS_TO
@@ -747,16 +755,8 @@ PATH_SEPARATOR
 SHELL
 WERROR_CFLAGS
 WARN_CFLAGS
-sim_reserved_bits
 sim_inline
-sim_hw
-sim_hw_objs
-sim_hw_cflags
-sim_default_model
-sim_scache
-sim_float
 sim_endian
-sim_bitsize
 sim_alignment'
 ac_subst_files=''
 ac_user_opts='
@@ -11791,7 +11791,6 @@ _ACEOF
 
 
 
-
 wire_endian="LITTLE"
 default_endian=""
 # Check whether --enable-sim-endian was given.
@@ -11999,6 +11998,18 @@ ac_config_commands="$ac_config_commands Makefile"
 
 ac_config_commands="$ac_config_commands stamp-h"
 
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 cat >confcache <<\_ACEOF
 # This file is a shell script that caches the results of configure
 # tests run on this system so they can be shared between configure