Yes, ineed it does help. Up-to-now I used the -Dtest_isolation_mode=prepare that with this fix can be safely removed.
Then I still define + -Dv8_enable_slow_dchecks=0 to fix otherwise breaking compilation:
Severity Code Description Project File Line Suppression State
Error C2373 'v8::internal::FLAG_enable_slow_asserts': redefinition; different type modifiers (compiling source file ..\build\Debug\obj\global_intermediate\libraries.cc) v8_nosnapshot v8\src\flag-definitions.h 983
Not that I mind stopping slow dchecks, just saying.
Again, thanks!