Add a unit test for an x86_64 assembly inspection of

a large stack frame with lots of spilled registers.

While writing the i386 version of this test, it looks
like I found a bug in the 32-bit instruction profiler
code.  I may ned to fix the assembly inspection engine
before I can finish writing that test, so I'm only
committing the 64-bit one tonight.

<rdar://problem/28509178> 

llvm-svn: 282683