clang-format syntax error in arch.c

Xref #2876 (closed)

See PR #3404 where clang-format-diff.py's local format (correctly) shifts hook_vsyscall's comment and surrounding functions to where they should be. clang-format hits a syntax error in get_ibl_routine_name() which messes up the subsequent formatting.

The plan is to redo get_ibl_routine_name() to address this.

There are some other places where something like this happens, including #3158 (closed)