scons: Add MARSHAL_XXFLAGS_EXTRA for the marshal object

We already provide to the user the CCFLAGS_EXTRA, LDFLAGS_EXTRA
variables to pass flags to scons when compiling/linking gem5.
Those variables are not passed to the marshal object.
We add an extra pair:

MARSHAL_CCFLAGS_EXTRA, MARSHAL_LDFLAGS_EXTRA

to add flag injection capabilities to the marshal object.

The patch is also renaming base_py_env to marshal_env.
This happens for 2 reasons:

1) At the moment the marshal compilation is the only task
making use of the base python environment.

2) Consistency with the EXTRA variable names added with this patch.
I could have named them as BASE_XXFLAGS_EXTRA, but it seems too much
generic and users might be confused by that, as they might think
the BASE_XXFLAGS_EXTRA is a subset of the XXFLAGS_EXTRA so that
setting it will affect gem5 compilation as well.

Change-Id: I3e420caa897059455ff8f35462db2b38da050e93
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/30016
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

SConstruct

diff --git a/SConstruct b/SConstruct
index 4bc3d0e..b327a8b 100755
--- a/SConstruct
+++ b/SConstruct
@@ -276,6 +276,8 @@
     ('CXX', 'C++ compiler', environ.get('CXX', main['CXX'])),
     ('CCFLAGS_EXTRA', 'Extra C and C++ compiler flags', ''),
     ('LDFLAGS_EXTRA', 'Extra linker flags', ''),
+    ('MARSHAL_CCFLAGS_EXTRA', 'Extra C and C++ marshal compiler flags', ''),
+    ('MARSHAL_LDFLAGS_EXTRA', 'Extra marshal linker flags', ''),
     ('PYTHON_CONFIG', 'Python config binary to use',
      [ 'python2.7-config', 'python-config', 'python3-config' ]),
     ('PROTOC', 'protoc tool', environ.get('PROTOC', 'protoc')),
@@ -734,7 +736,9 @@
 
 main.Prepend(CPPPATH=Dir('ext/pybind11/include/'))
 # Bare minimum environment that only includes python
-base_py_env = main.Clone()
+marshal_env = main.Clone()
+marshal_env.Append(CCFLAGS='$MARSHAL_CCFLAGS_EXTRA')
+marshal_env.Append(LINKFLAGS='$MARSHAL_LDFLAGS_EXTRA')
 
 # On Solaris you need to use libsocket for socket ops
 if not conf.CheckLibWithHeader(None, 'sys/socket.h', 'C++', 'accept(0,0,0);'):
@@ -1285,7 +1289,7 @@
     # to the configured variables.  It returns a list of environments,
     # one for each variant build (debug, opt, etc.)
     SConscript('src/SConscript', variant_dir=variant_path,
-               exports=['env', 'base_py_env'])
+               exports=['env', 'marshal_env'])
 
 # base help text
 Help('''