util: Add an "args" unit test to the m5 utility.

Change-Id: I7460daaff3301b09e071f2b7e8fb657909805438
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27560
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

util/m5/src/SConscript.native

@@ -24,3 +24,5 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 Import('*')
+
+env.GTest('args')