sim: testsuite: push $arch out to targets

This is needed to move to automake & its dejagnu-provided logic,
and eventually by the unified sim logic.  The $arch is used only
to figure out which `run` program to use when running tests, and
as we move to a single top-level build, we can delete this and
use sim/run directly.

sim/testsuite/m32c/ChangeLog

@@ -1,3 +1,7 @@
+2021-02-13  Mike Frysinger  <vapier@gentoo.org>
+
+	* allinsn.exp: Define arch.
+
 2015-11-14  Mike Frysinger  <vapier@gentoo.org>
 
 	* allinsn.exp: New file.

sim/testsuite/m32c/allinsn.exp

@@ -2,6 +2,10 @@
 # TODO: Add support for .c tests.
 
 if [istarget m32c*-*-*] {
+    # Used to locate the `run` program.
+    global arch
+    set arch "m32c"
+
     # all machines
     set all_machs "m32c"