Fix the CheckerCPU being included via python.

src/arch/SConscript:
    Fixes for including the CheckerCPU if it's specified via command line.  Previously the env variable was actually being modified.
src/cpu/SConscript:
    Copy the CPU_MODELS from the env, don't create a proxy to it.

--HG--
extra : convert_revision : 7d069bd93a6834ccaa1c378b2bc76dce76745c19

src/cpu/SConscript

@@ -71,7 +71,8 @@ virtual Fault completeAcc(uint8_t *data, %s *xc, Trace::InstRecord *traceData) c
 # Generate a temporary CPU list, including the CheckerCPU if
 # it's enabled.  This isn't used for anything else other than StaticInst
 # headers.
-temp_cpu_list = env['CPU_MODELS']
+temp_cpu_list = env['CPU_MODELS'][:]
+
 if env['USE_CHECKER']:
     temp_cpu_list.append('CheckerCPU')