This patch fixes https://github.com/llvm/llvm-project/issues/187033
In BE8 mode, instruction bytes are reversed for sections containing
code. This logic currently assumes that arm mapping symbols (e.g. $a,
$t, $d) are always associated with InputSections.
However, mapping symbols can also be defined in other section types such
as mergeable sections (SHF_MERGE). These are not represented as
InputSection, and attempting to cast them using
cast_if_present<InputSection> results in an assertion failure.
dc9be4ee30