Errors when trying to generate a test coverage report

I tried to generate a test coverage report and ran into an entire zoo of errors.
I'll describe the issues so we can try to get this fixed, and a workaround. Skip to the end for the workaround.

### Issue 1

Let's start with
```
$ cabal test intmap-lazy-properties --enable-coverage
<...>
[ 5 of 37] Compiling Utils.Containers.Internal.PtrEquality ( <...> )

: error:
compiler/GHC/StgToCmm/Prim.hs:(344,32)-(345,74): Non-exhaustive patterns in lambda

Error: cabal: Failed to build containers-0.6.8 (which is required by
containers-tests-0).
```

The locations leads us to the `emitPrimop` for `ReallyUnsafePtrEqualityOp`.
https://gitlab.haskell.org/ghc/ghc/-/blob/ghc-9.6/compiler/GHC/StgToCmm/Prim.hs?ref_type=heads#L344-345

I am baffled.

Let's continue with a workaround, by removing all the `reallyUnsafePtrEquality#` stuff in `PtrEquality.hs`.

### Issue 2

```
$ cabal test intmap-lazy-properties --enable-coverage
<...>
Running 1 test suites...
Test suite intmap-lazy-properties: RUNNING...
Test suite intmap-lazy-properties: PASS
Test suite logged to:
/home/meooow/dev/containers/dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-tests-0/test/containers-tests-0-intmap-lazy-properties.log
hpc-ghc-9.6.3: can not find containers-0.6.8-inplace/Utils.Containers.Internal.StrictPair in ./.hpc, /home/meooow/dev/containers/dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-tests-0/hpc/vanilla/mix/containers-tests-0, /home/meooow/dev/containers/dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-tests-0/hpc/vanilla/mix/intmap-lazy-properties
CallStack (from HasCallStack):
error, called at libraries/hpc/Trace/Hpc/Mix.hs:122:15 in hpc-0.6.2.0:Trace.Hpc.Mix
Error: cabal: Tests failed for containers-tests-0.
```

Okay we got the tests to run successfully. But hpc failed.
I find that I have two `vanilla/mix` dirs:
* dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-tests-0/hpc/vanilla/mix
* dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-0.6.8/hpc/vanilla/mix

For some reason, hpc attempts to find `containers-0.6.8` mix files without being aware of the `containers-0.6.8` directory. This looks like a Cabal issue? Let's try to work around it by running hpc manually.

### Using hpc

I had to jump through a few hoops with hpc but they aren't really bugs so I won't go into the details. The gist is that I needed to go into containers-test and run hpc providing the tix file and mix dirs manually.

```
$ cd containers-tests
$ hpc markup \
../dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-tests-0/hpc/vanilla/tix/intmap-lazy-properties/intmap-lazy-properties.tix \
--hpcdir ../dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-tests-0/hpc/vanilla/mix/containers-tests-0 \
--hpcdir ../dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-tests-0/hpc/vanilla/mix/intmap-lazy-properties \
--hpcdir ../dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-0.6.8/hpc/vanilla/mix/containers-0.6.8
Writing: containers-0.6.8-inplace/Utils.Containers.Internal.Coercions.hs.html
<...>
Writing: IntMapValidity.hs.html
Writing: hpc_index.html
Writing: hpc_index_fun.html
Writing: hpc_index_alt.html
Writing: hpc_index_exp.html
```

Success!

### Workaround tl;dr

1. Delete the imports and usages of `reallyUnsafePtrEquality#` in `PtrEquality.hs`
2. Run the test with `cabal test intmap-lazy-properties --enable-coverage`. The test will run but hpc will fail, that's fine.
3. `cd containers-tests`
4. Run hpc providing the tix file and mix dirs
```
hpc markup \
../dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-tests-0/hpc/vanilla/tix/intmap-lazy-properties/intmap-lazy-properties.tix \
--hpcdir ../dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-tests-0/hpc/vanilla/mix/containers-tests-0 \
--hpcdir ../dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-tests-0/hpc/vanilla/mix/intmap-lazy-properties \
--hpcdir ../dist-newstyle/build/x86_64-linux/ghc-9.6.3/containers-0.6.8/hpc/vanilla/mix/containers-0.6.8
```