[clang] [clang] Fix assertion failure when printing atomic apvalues (PR #85259)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

LGTM but this should be testable because `getAsString()` uses `printPretty()`: https://github.com/llvm/llvm-project/blob/e6f63a942a45e3545332cd9a43982a69a4d5667b/clang/lib/AST/Interp/FunctionPointer.h#L53, https://github.com/llvm/llvm-project/blob/e6f63a942a45e3545332cd9a43982a69a4d5667b/clang/lib/AST/ExprConstant.cpp#L1674, etc

https://github.com/llvm/llvm-project/pull/85259