tests, base: Added GTests for base/amo.hh

Issue-on: https://gem5.atlassian.net/browse/GEM5-231

Change-Id: Ia915f9c8bd0732c6c918e8056253bd2fdcdf6b5d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26944
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/base/SConscript

@@ -29,6 +29,7 @@
 Import('*')
 
 SimObject('Graphics.py')
+GTest('amo.test', 'amo.test.cc')
 Source('atomicio.cc')
 GTest('atomicio.test', 'atomicio.test.cc', 'atomicio.cc')
 Source('bitfield.cc')