scons: Fix grpc protobuf actions

The change will fix the proto import issue and build issue with
--no-duplicate-sources options, more details please reference:
https://gem5-review.googlesource.com/c/public/gem5/+/64491.

Change-Id: I259413f7739f89598dcd42c3f2e1e865cec3de43
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/71318
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

@@ -280,9 +280,9 @@ def protoc_grpc_emitter(target, source, env):
     root, ext = os.path.splitext(source[0].get_abspath())
     return [root + '.grpc.pb.cc', root + '.grpc.pb.h'], source
 
-protoc_grpc_action=MakeAction('${PROTOC} --grpc_out ${BUILDDIR} '
-        '--plugin=protoc-gen-grpc=${PROTOC_GRPC} --proto_path ${BUILDDIR} '
-        '${SOURCE.get_abspath()}',
+protoc_grpc_action=MakeAction('${PROTOC} --grpc_out ${TARGET.dir.abspath} '
+        '--plugin=protoc-gen-grpc=${PROTOC_GRPC} '
+        '--proto_path ${SOURCE.dir.abspath} ${SOURCE.abspath}',
         Transform("PROTOC"))
 
 env.Append(BUILDERS={'GrpcProtoBufCC' : Builder(