Enable building only selected CPU models via new scons

CPU_MODELS parameter.  For example:
scons CPU_MODELS="SimpleCPU,FullCPU" ALPHA_SE/m5.debug
Unfortunately the option is not sticky due to a scons
bug with saving & restoring ListOption parameters.

SConscript:
    Separate out cpu-model-specific files so they can be conditionally
    included based on value of new CPU_MODELS parameter.
    Most of these are now handled in cpu/SConscript, except for FullCPU
    which is still in this file.
arch/SConscript:
    The set of CPU-model-specific execute files must now be
    determined from the CPU_MODELS parameter, via the new
    cpu_models.py file.
    Also pass the list of configured CPU models to isa_parser.py.
arch/isa_parser.py:
    Move CpuModel definition and objects out to a
    separate file so they can be shared with scons.
    Global list of CPU models to generate code for is now
    controlled by command-line parameters (so we can do
    only a subset of the available ones).
build/SConstruct:
    Define new CPU_MODELS ListOption.
cpu/static_inst.hh:
    Rename static_inst_impl.hh to static_inst_exec_sigs.hh.

--HG--
extra : convert_revision : 163df32a76d4c05900490b2bce4c7962a5e3f614

arch/SConscript

@@ -108,26 +108,27 @@ env.Append(SCANNERS = iscan)
 # output from the ISA description (*.isa) files.
 #
 
-# several files are generated from the ISA description
-isa_desc_gen_files = Split('''
-	decoder.cc
-        alpha_o3_exec.cc
-	fast_cpu_exec.cc
-        simple_cpu_exec.cc
-        full_cpu_exec.cc
-	decoder.hh
-        ''')
-
 # Convert to File node to fix path
 isa_parser = File('isa_parser.py')
+cpu_models_file = File('#m5/cpu/cpu_models.py')
+
+# This sucks in the defintions of the CpuModel objects.
+execfile(cpu_models_file.srcnode().abspath)
+
+# Several files are generated from the ISA description.
+# We always get the basic decoder and header file.
+isa_desc_gen_files = Split('decoder.cc decoder.hh')
+# We also get an execute file for each selected CPU model.
+isa_desc_gen_files += [CpuModel.dict[cpu].filename
+                       for cpu in env['CPU_MODELS']]
 
 # 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):
-    return (isa_desc_gen_files, [isa_parser] + source)
+    return (isa_desc_gen_files, [isa_parser, cpu_models_file] + source)
 
 # Pieces are in place, so create the builder.
-isa_desc_builder = Builder(action='${SOURCES[0]} ${SOURCES[1]} $TARGET.dir',
+isa_desc_builder = Builder(action='$SOURCES $TARGET.dir $CPU_MODELS',
                            source_scanner = iscan,
                            emitter = isa_desc_emitter)