Parallelize LLVMPointsToSet

[blipper]

Is your feature request related to a problem? Please describe.
For programs with large numbers of variables and functions O(thouands) LLVMPointsToSet takes O(minutes) even with CDLSheen.

Describe the solution you'd like
Parallelize this using the cores on the machine! It seems like it is somewhat possible even if only to call AA.alias() in parallel - which takes most of the time?

Describe alternatives you've considered
Dunno?

[blipper]

Metrics for the output

00:00:13.734705 - [INFO] Preprocess module: /tmp/aes_ctr_boringssl_test.bc
00:00:13.735430 - [INFO] Running ValueAnnotationPass
00:00:21.333130 - [INFO] Running GeneralStatisticsAnalysis
00:00:22.906208 - [INFO] GeneralStatisticsAnalysis summary for module: '/tmp/aes_ctr_boringssl_test.bc'
00:00:22.906314 - [INFO] Instructions : 2142062
00:00:22.906344 - [INFO] Allocated Types : 1012
00:00:22.906393 - [INFO] Allocation Sites : 21274
00:00:22.906425 - [INFO] Basic Blocks : 212656
00:00:22.906451 - [INFO] Calls Sites : 1039358
00:00:22.906493 - [INFO] Functions : 16581
00:00:22.906518 - [INFO] Globals : 20123
00:00:22.906541 - [INFO] Global Pointer : 20123
00:00:22.906564 - [INFO] Memory Intrinsics : 10438
00:00:22.906588 - [INFO] Store Instructions : 80218

[blipper]

Adding draft implementation in #309 and #310

[blipper]

This will likely be dependent on #319