[clang] [Clang][CodeGen] Use ptrtoaddr for pointer diff (PR #210729)

[Devon Loehr via cfe-commits]

DKLoehr wrote:

We've started seeing `RangeAdapterTest`s failing on some of our chromium CI bots, and reverting this comment fixes it. Unfortunately, we've so far been unable to reproduce off of the bot, so we don't have a standalone example of how things go wrong. It only seems to be happening on arm macs, and only in the second stage of bootstrap builds. That is, the initial compiler we build passes the tests; when we use that bootstrapped clang to build clang again, the test starts failing.

For context, this is the [chromium bug](https://crbug.com/549079131), and this [build log](https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket/8673054152294541633/+/u/package_clang/stdout?format=raw) shows the failure. I'll also paste the output here. I'm trying to get some kind of standalone reproducer, but figured it was better to report early in case it sparks something on its own.

In addition to bootstrapping, we're building with PGO enabled, and optimizations disabled.

<details>
  <summary>Error text</summary>
  
 ```
 Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90
 FAIL: LLVM-Unit :: ADT/./ADTTests/31/35 (92462 of 99378)
 ******************** TEST 'LLVM-Unit :: ADT/./ADTTests/31/35' FAILED ********************
 Script(shard):
 --
 GTEST_OUTPUT=json:/Volumes/Work/s/w/ir/cache/builder/src/third_party/llvm-build/Release+Asserts/unittests/ADT/./ADTTests-LLVM-Unit-21639-31-35.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=35 GTEST_SHARD_INDEX=31 /Volumes/Work/s/w/ir/cache/builder/src/third_party/llvm-build/Release+Asserts/unittests/ADT/./ADTTests
 --
 
 Script:
 --
 /Volumes/Work/s/w/ir/cache/builder/src/third_party/llvm-build/Release+Asserts/unittests/ADT/./ADTTests --gtest_filter=RangeAdapterLValueTest/0.TrivialOperation
 --
 /Volumes/Work/s/w/ir/cache/builder/src/third_party/llvm/llvm/unittests/ADT/RangeAdapterTest.cpp:123: Failure
 Expected equality of these values:
   i
     Which is: 0
   counter--
     Which is: 3
 
 /Volumes/Work/s/w/ir/cache/builder/src/third_party/llvm/llvm/unittests/ADT/RangeAdapterTest.cpp:123: Failure
 Expected equality of these values:
   i
     Which is: 0
   counter--
     Which is: 2
 
 
 /Volumes/Work/s/w/ir/cache/builder/src/third_party/llvm/llvm/unittests/ADT/RangeAdapterTest.cpp:123
 Expected equality of these values:
   i
     Which is: 0
   counter--
     Which is: 3
 
 /Volumes/Work/s/w/ir/cache/builder/src/third_party/llvm/llvm/unittests/ADT/RangeAdapterTest.cpp:123
 Expected equality of these values:
   i
     Which is: 0
   counter--
     Which is: 2
 ```
  
</details>

https://github.com/llvm/llvm-project/pull/210729