PowerPC: tests `decodeMyStack` and `decodeMyStack_underflowFrames` fail

Issue

Tests decodeMyStack and decodeMyStack_underflowFrames fail on powerpc64 big-endian and little-endian. The output for decodeMyStack contains several lines like this:

...
-StackEntry {functionName = "getDeepStack.getDeepStackCase", moduleName = "Main", srcLoc = "decodeMyStack.hs:13:7-21", closureType = 53}
+StackEntry {functionName = "", moduleName = "Main", srcLoc = "", closureType = 53}
...

In all StackEntrys there is an empty functionName and srcLoc.

The test was introduced in 29717ecb and some of the functionality in 6f7f5990.

Environment

• GHC version used: HEAD at 44a5507f.

Optional:

• Operating System: openSUSE Leap 15.2 powerpc64le and Void Linux powerpc64
• System Architecture: powerpc64le and powerpc64 (big-endian)