[CaptureTracker] Provide an ordered basic block to PointerMayBeCapturedBefore

This patch is a follow up from r240560 and is a step further into
mitigating the compile time performance issues in CaptureTracker.

By providing the CaptureTracker with a "cached ordered basic block"
instead of computing it every time, MemDepAnalysis can use this cache
throughout its calls to AA->callCapturesBefore, avoiding to recompute it
for every scanned instruction. In the same testcase used in r240560,
compile time is reduced from 2min to 30s.

This also fixes PR22348.

rdar://problem/19230319
Differential Revision: http://reviews.llvm.org/D11364

llvm-svn: 243750