configure.py: make messaging_service.cc the first source file

Currently messaging_service.o takes the longest of all core objects to
compile.  For a full build of build/release/scylla, with current ninja
scheduling, on a 32-hyperthread machine, the last ~16% of the total
build time is spent just waiting on messaging_service.o to finish
compiling.

Moving the file to the top of the list makes ninja start its compilation
early and gets rid of that single-threaded tail, improving the total build
time.

Closes scylladb#11255

configure.py

@@ -673,7 +673,8 @@ def find_headers(repodir, excluded_dirs):
     'raft/log.cc',
 ]
 
-scylla_core = (['replica/database.cc',
+scylla_core = (['message/messaging_service.cc',
+                'replica/database.cc',
                 'replica/table.cc',
                 'replica/distributed_loader.cc',
                 'replica/memtable.cc',
@@ -949,7 +950,6 @@ def find_headers(repodir, excluded_dirs):
                 'locator/ec2_snitch.cc',
                 'locator/ec2_multi_region_snitch.cc',
                 'locator/gce_snitch.cc',
-                'message/messaging_service.cc',
                 'service/client_state.cc',
                 'service/storage_service.cc',
                 'service/misc_services.cc',