Fix up code to be able to use the Checker.

SConstruct:
    Remove check for Checker from this SConstruct
src/arch/SConscript:
    Specific check if CheckerCPU is being used.  Not the cleanest, but works for now.
src/cpu/SConscript:
    Code to handle using the CheckerCPU a little better.  Allows -c to be used normally.

--HG--
extra : convert_revision : 0a82f16db0f38e5ce114d08368477bd211331fa3

src/arch/SConscript

@@ -128,6 +128,11 @@ isa_desc_gen_files = Split('decoder.cc decoder.hh')
 isa_desc_gen_files += [CpuModel.dict[cpu].filename
                        for cpu in env['CPU_MODELS']]
 
+# Also include the CheckerCPU as one of the models if it is being
+# enabled via command line.
+if env['USE_CHECKER']:
+    isa_desc_gen_files += [CpuModel.dict['CheckerCPU'].filename]
+
 # The emitter patches up the sources & targets to include the
 # autogenerated files as targets and isa parser itself as a source.
 def isa_desc_emitter(target, source, env):