python: Ensure that m5.internal.params is available

Add an import to m5.internal.params which became necessary after:

95f9017c2e configs,python: Clean some cruft out of m5.objects.

This import is necessary but also causes problems when scons calls
build_tools/sim_object_param_struct_hh.py to generate
params/SimObject.hh. m5.internal.params itself imports _m5 and _m5 is
unavalailable resulting in an ImportError. This is bening and we can
safely ignore it.

Change-Id: I3809e81284e730fb9c9e0e7e91bd61b801d73f90
Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/67797
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>

src/python/m5/SimObject.py

@@ -445,6 +445,9 @@ class MetaSimObject(type):
         return cls.__name__
 
     def getCCClass(cls):
+        # Ensure that m5.internal.params is available.
+        import m5.internal.params
+
         return getattr(m5.internal.params, cls.pybind_class)
 
     # See ParamValue.cxx_predecls for description.

src/python/m5/internal/params.py

@@ -37,8 +37,17 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 import inspect
-import _m5
 
-for name, module in inspect.getmembers(_m5):
-    if name.startswith("param_") or name.startswith("enum_"):
-        exec("from _m5.%s import *" % name)
+try:
+    # Avoid ImportErrors at build time when _m5 is not available
+    import _m5
+
+    in_gem5 = True
+except ImportError:
+    # The import failed, we're being called from the build system
+    in_gem5 = False
+
+if in_gem5:
+    for name, module in inspect.getmembers(_m5):
+        if name.startswith("param_") or name.startswith("enum_"):
+            exec("from _m5.%s import *" % name)