Add file hash to .debug_line #936
Description
The file hash can be used by a debugger to detect when the source file has changed after compilation.
This can be implemented by passing a FileInfo the right MD5 hash to LineProgram::new and line_program.add_file (here and here) and setting line_program.file_has_md5 to true. Also the DWARF version on platforms other than macOS needs to be changed to 5.
Blocked on rust-lang/rust#69718, which implements this for cg_llvm and adds a new src_hash field to SourceFile storing the MD5 hash.