cmake: Use Policy CMP0117 for more sensible RTTI flag configuration on MSVC.

CMake/RemoveCompileFlag.cmake

@@ -0,0 +1,16 @@
+# from https://stackoverflow.com/a/49216539
+# The linked answer does some weird preconfiguring by manually splitting the CMAKE_CXX_FLAGS variable and applying it to a target,
+# but as far as I can tell none of that is necessary, this works just fine as-is.
+
+#
+# Removes the specified compile flag from the specified target.
+#   _target     - The target to remove the compile flag from
+#   _flag       - The compile flag to remove
+#
+macro(remove_cxx_flag_from_target _target _flag)
+    get_target_property(_target_cxx_flags ${_target} COMPILE_OPTIONS)
+    if(_target_cxx_flags)
+        list(REMOVE_ITEM _target_cxx_flags ${_flag})
+        set_target_properties(${_target} PROPERTIES COMPILE_OPTIONS "${_target_cxx_flags}")
+    endif()
+endmacro()