Startup speedup: scons decider (#2309)

* dump timing

* fix

* change a bit

* change a bit

* change a bit

* improve scons

* fix typo

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* try to improve manager

* change decider

* reduce diff

* reduce diff

* reduce diff

* reduce diff and fix review

* submodules
old-commit-hash: d53129324573f9e2d2539284c6f20ff18eefc3cf

SConstruct

@@ -7,6 +7,7 @@ import sys
 import platform
 
 TICI = os.path.isfile('/TICI')
+Decider('MD5-timestamp')
 
 AddOption('--test',
           action='store_true',