On RISC-V, clang emits empty name symbols used for label differences. (In GCC the symbols are typically .L0)
After D95916, the empty name symbols can show up in llvm-symbolizer's symbolization output.
They have no names and thus not useful. Set SF_FormatSpecific so that llvm-symbolizer will ignore them.
SF_FormatSpecific is also used in LTO but that case should not matter.
Corresponding addr2line problem: https://sourceware.org/bugzilla/show_bug.cgi?id=27585