This is not very useful in itself, but makes it possible to detect this
address in the output. See the next commit.
This adds around 50 bytes to each binary (except for AVR and wasm). This
is unfortunate, but I think this feature is quite useful still.
A future enhancement might be to create a build tag for extended panic
information that's not set by default.
This test only applies when using the built-in LLVM version. This way,
we have a stable LLVM version to test against. Distribution versions of
LLVM (especially Debian) tend to be patched in a way that affect the
results.
