Add elapsed time print statement to build system

(cherry picked from commit d07015909496be8eed7cbadc159ef0054565d5ef)

SConstruct

@@ -3,10 +3,12 @@
 EnsureSConsVersion(0, 98, 1)
 
 # System
+import atexit
 import glob
 import os
 import pickle
 import sys
+import time
 from collections import OrderedDict
 
 # Local
@@ -25,6 +27,8 @@ active_platform_ids = []
 platform_exporters = []
 platform_apis = []
 
+time_at_start = time.time()
+
 for x in sorted(glob.glob("platform/*")):
     if not os.path.isdir(x) or not os.path.exists(x + "/detect.py"):
         continue
@@ -676,3 +680,12 @@ if "env" in locals():
     # TODO: replace this with `env.Dump(format="json")`
     # once we start requiring SCons 4.0 as min version.
     methods.dump(env)
+
+
+def print_elapsed_time():
+    elapsed_time_sec = round(time.time() - time_at_start, 3)
+    time_ms = round((elapsed_time_sec % 1) * 1000)
+    print(f"[Time elapsed: {time.strftime('%H:%M:%S', time.gmtime(elapsed_time_sec))}.{time_ms:03}]")
+
+
+atexit.register(print_elapsed_time)