build: Silence C4996 warnings on Visual Studio due to legacy TBB

The containers in TBB versions prior to oneTBB use iterators that
derive from std::iterator. This causes Visual Studio to issue a
STL4015 warning noting that std::iterator is deprecated in C++17.

Since this warning is due to third-party code, we can't do much
about it, so we just silence the warning in our build configuration.
This removes 33 out of 63 warnings.

Note that these warnings show up even though CMake is (AFAICT) using
Visual Studio's /external feature to disable warnings from external
headers. Not sure what's going on there...

(Internal change: 2389464)

Author: sunyab

cmake/defaults/msvcdefaults.cmake

@@ -91,6 +91,10 @@ _add_define("_CRT_SECURE_NO_WARNINGS")
 # std::copy, std::equal, et al.
 _add_define("_SCL_SECURE_NO_WARNINGS")
 
+# Disable warning C4996 regarding use of std::iterator as a base class.
+# This warning is emitted from legacy TBB's containers/iterators.
+_add_define("_SILENCE_CXX17_ITERATOR_BASE_CLASS_DEPRECATION_WARNING")
+
 # Make sure WinDef.h does not define min and max macros which
 # will conflict with std::min() and std::max().
 _add_define("NOMINMAX")