scons: Add -rdynamic when building python embed binary

When you build Python from scratch, the modules would be separated
shared libraries. They would be dlopen when doing module import. To make
the separated shared libraries can share the symbol in the binary, we
should add -rdynamic when compliing.

Change-Id: I26bf9fd7ea5068fd2d08c8f059b37ff34073e8c2
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/72040
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>

src/SConscript

@@ -626,6 +626,7 @@ PySource('m5', 'python/m5/info.py')
 gem5py_m5_env = gem5py_env.Clone()
 gem5py_env.Append(CPPPATH=env['CPPPATH'])
 gem5py_env.Append(LIBS='z')
+gem5py_env.Append(LINKFLAGS='-rdynamic')
 gem5py_env.Program(gem5py, 'python/gem5py.cc')[0]
 m5_module_source = \
         Source.all.with_all_tags(env, 'm5_module', 'gem5 lib')
@@ -647,6 +648,7 @@ env.AlwaysBuild(tags)
 #
 
 env['SHOBJSUFFIX'] = '${OBJSUFFIX}s'
+env.Append(LINKFLAGS='-rdynamic')
 
 envs = {
     'debug': env.Clone(ENV_LABEL='debug', OBJSUFFIX='.do'),