Let FBVector.h support -fno-exceptions
Let FBVector.h support -fno-exceptions

Summary: [Folly] Let `folly/FBVector.h` support `-fno-exceptions`. Same mechanism as with `folly/small_vector.h`.

Reviewed By: Orvid

Differential Revision: D15158754

fbshipit-source-id: fe67d608a5b38258d05718efae502b7277e1f4ee

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly