sim: split sim-signal.h include out

The sim-basics.h is too big and includes too many things.  This leads
to some arch's sim-main.h having circular loop issues with defs, and
makes it hard to separate out common objects from arch-specific defs.
By splitting up sim-basics.h and killing off sim-main.h, it'll make
it easier to separate out the two.

sim/mips/ChangeLog

@@ -1,3 +1,7 @@
+2021-06-18  Mike Frysinger  <vapier@gentoo.org>
+
+	* interp.c: Include sim-signal.h.
+
 2021-06-17  Mike Frysinger  <vapier@gentoo.org>
 
 	* configure.ac: Delete SIM_AC_OPTION_ENDIAN call.

sim/mips/interp.c

@@ -31,6 +31,7 @@ code on the hardware.
 #include "sim-options.h"
 #include "sim-assert.h"
 #include "sim-hw.h"
+#include "sim-signal.h"
 
 #include "itable.h"