Use a BumpPtrAllocator to allocate all aspects of CFG, including CFGBlocks,...

Use a BumpPtrAllocator to allocate all aspects of CFG, including CFGBlocks, successor and predecessor vectors, etc.

Speedup: when doing 'clang-cc -analyze -dump-cfg' (without actual printing, just
CFG building) on the amalgamated SQLite source (all of SQLite in one source
file), runtime reduced by 9%.

This fixes: <rdar://problem/7250745>

llvm-svn: 83899