Portable debug symbol table without libbfd requirement?

rts/Printer.c implements various heap printing functions that are used by the debug RTS. When it comes to printing a pointer, it might be a static data/function entity associated with a symbol, and printing the symbol instead of an opaque hex pointer would be much more helpful to debugging.

As of today, if you configure GHC with --enable-bfd-debug, then the debug RTS would link against libbfd and use that to parse the Haskell executable itself and extract symbol info. libbfd has a number of backends representing what binaries it can parse, ELF/COFF is included, but some other modern formats are not (e.g. Mach-O or wasm).

It's actually pretty simple to implement a portable debug symbol table mechanism that works on any target that links the C RTS. We can add a GHC flag to emit a special constructor for each module to update the RTS debug symbol table with mappings from symbols to their name strings. Compared to libbfd, this is slightly more limited on Linux since the C foreign symbols will be missing, but the majority of the symbols dumped by Printer.c are Haskell/Cmm entities anyway, so a portable implementation still improves the status quo a lot.