[ADT][BitVector] Add push_back()

Add a higher performance alternative to calling resize() every time which performs a lot of clearing to zero - when we're adding a single bit most of the time this will be completely unnecessary.

Differential Revision: https://reviews.llvm.org/D52236

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342535 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed