Mandatory "distinct" for DISubprogram and DICompileUnit

[langston-barrett]

When attempting to re-assemble this file with llvm-as from LLVM 6 after disassembling it with llvm-pretty/llvm-pretty-bc-parser, I get the following complaint:

$ nix-shell --pure -p llvm_6 --run "llvm-as /run/user/1000/cfi-eof-prologue.newllvm-disasm24413-2.ll"                                                        
llvm-as: /run/user/1000/cfi-eof-prologue.newllvm-disasm24413-2.ll:158:40: error: missing 'distinct', required for !DICompileUnit                             
                       templateParams: !DICompileUnit(language: 4, file: !3,
                                       ^

Unfortunately, my first attempt to fix this (putting "distinct" in the indicated location) failed:

$ nix-shell --pure -p llvm_6 --run "llvm-as /run/user/1000/cfi-eof-prologue.newllvm-disasm24413-2.ll"                                                        
llvm-as: /run/user/1000/cfi-eof-prologue.newllvm-disasm24413-2.ll:158:40: error: expected metadata operand                                                   
                       templateParams: distinct !DICompileUnit(language: 4, file: !3,  

Notice that in the relevant LLVM commit, they never have a DICompileUnit inline. My hypothesis is that this is a bug in their parser (they assume they never see DICompileUnit inline). However, we might just want to always output those on their own line.