[X86DomainReassignment] Don't compare stack-allocated values by address

Summary:
The Closure allocated in the main loop is allocated on the stack. However,
later in the code its address is taken (and used for comparisons). This
obviously doesn't work. In fact, the Closure will get the same stack address
during every loop iteration, rendering the check that intended to identify
Closure conflicts entirely ineffective. Fix this bug by giving every Closure
a unique ID and using that for comparison. Alternatively, we could heap
allocate the closure object.

Fixes PR37396
Fixes JuliaLang/julia#27032

Reviewers: craig.topper, guyblank

Reviewed By: craig.topper

Subscribers: vchuravy, llvm-commits

Differential Revision: https://reviews.llvm.org/D46800

llvm-svn: 332682