DI: Require subprogram definitions to be distinct

As a follow-up to r246098, require `DISubprogram` definitions
(`isDefinition: true`) to be 'distinct'.  Specifically, add an assembler
check, a verifier check, and bitcode upgrading logic to combat testcase
bitrot after the `DIBuilder` change.

While working on the testcases, I realized that
test/Linker/subprogram-linkonce-weak-odr.ll isn't relevant anymore.  Its
purpose was to check for a corner case in PR22792 where two subprogram
definitions match exactly and share the same metadata node.  The new
verifier check, requiring that subprogram definitions are 'distinct',
precludes that possibility.

I updated almost all the IR with the following script:

    git grep -l -E -e '= !DISubprogram\(.* isDefinition: true' |
    grep -v test/Bitcode |
    xargs sed -i '' -e 's/= \(!DISubprogram(.*, isDefinition: true\)/= distinct \1/'

Likely some variant of would work for out-of-tree testcases.

llvm-svn: 246327
diff --git a/llvm/test/DebugInfo/two-cus-from-same-file.ll b/llvm/test/DebugInfo/two-cus-from-same-file.ll
index 807eb83..4aeaaac 100644
--- a/llvm/test/DebugInfo/two-cus-from-same-file.ll
+++ b/llvm/test/DebugInfo/two-cus-from-same-file.ll
@@ -38,13 +38,13 @@
 !0 = distinct !DICompileUnit(language: DW_LANG_C99, producer: "clang version 3.2 (trunk 156513)", isOptimized: true, emissionKind: 1, file: !32, enums: !1, retainedTypes: !1, subprograms: !3, globals: !1, imports: !1)
 !1 = !{}
 !3 = !{!5}
-!5 = !DISubprogram(name: "foo", line: 5, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: true, scopeLine: 5, file: !32, scope: !6, type: !7, function: void ()* @foo, variables: !1)
+!5 = distinct !DISubprogram(name: "foo", line: 5, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: true, scopeLine: 5, file: !32, scope: !6, type: !7, function: void ()* @foo, variables: !1)
 !6 = !DIFile(filename: "foo.c", directory: "/tmp")
 !7 = !DISubroutineType(types: !8)
 !8 = !{null}
 !9 = distinct !DICompileUnit(language: DW_LANG_C99, producer: "clang version 3.2 (trunk 156513)", isOptimized: true, emissionKind: 1, file: !32, enums: !1, retainedTypes: !1, subprograms: !10, globals: !1, imports: !1)
 !10 = !{!12}
-!12 = !DISubprogram(name: "main", line: 11, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: true, scopeLine: 11, file: !32, scope: !6, type: !13, function: i32 (i32, i8**)* @main, variables: !19)
+!12 = distinct !DISubprogram(name: "main", line: 11, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: true, scopeLine: 11, file: !32, scope: !6, type: !13, function: i32 (i32, i8**)* @main, variables: !19)
 !13 = !DISubroutineType(types: !14)
 !14 = !{!15, !15, !16}
 !15 = !DIBasicType(tag: DW_TAG_base_type, name: "int", size: 32, align: 32, encoding: DW_ATE_signed)