sim: Add a unit test for the GuestABI mechanism.

Jira Issue: https://gem5.atlassian.net/browse/GEM5-187

Change-Id: I76934d94b4c61570a4ca603388012c65280e2b7c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23197
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/sim/SConscript

@@ -78,6 +78,7 @@ Source('clocked_object.cc')
 Source('mathexpr.cc')
 
 GTest('byteswap.test', 'byteswap.test.cc', '../base/types.cc')
+GTest('guest_abi.test', 'guest_abi.test.cc')
 
 if env['TARGET_ISA'] != 'null':
     SimObject('InstTracer.py')