llvm: update ffi bindings for split dwarf

This commit modifies the FFI bindings to LLVM required for Split DWARF
support in rustc. In particular:

- `addPassesToEmitFile`'s wrapper, `LLVMRustWriteOutputFile` now takes
  a `DwoPath` `const char*`. When disabled, `nullptr` should be provided
  which will preserve existing behaviour. When enabled, the path to the
  `.dwo` file should be provided.
- `createCompileUnit`'s wrapper, `LLVMRustDIBuilderCreateCompileUnit`
  now has two additional arguments, for the `DWOId` and to enable
  `SplitDebugInlining`. `DWOId` should always be zero.
- `createTargetMachine`'s wrapper, `LLVMRustCreateTargetMachine` has an
  additional argument which should be provided the path to the `.dwo`
  when enabled.

Signed-off-by: David Wood <david@davidtw.co>

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -690,13 +690,14 @@ extern "C" LLVMMetadataRef LLVMRustDIBuilderCreateCompileUnit(
     const char *Producer, size_t ProducerLen, bool isOptimized,
     const char *Flags, unsigned RuntimeVer,
     const char *SplitName, size_t SplitNameLen,
-    LLVMRustDebugEmissionKind Kind) {
+    LLVMRustDebugEmissionKind Kind,
+    uint64_t DWOId, bool SplitDebugInlining) {
   auto *File = unwrapDI<DIFile>(FileRef);
 
   return wrap(Builder->createCompileUnit(Lang, File, StringRef(Producer, ProducerLen),
                                          isOptimized, Flags, RuntimeVer,
                                          StringRef(SplitName, SplitNameLen),
-                                         fromRust(Kind)));
+                                         fromRust(Kind), DWOId, SplitDebugInlining));
 }
 
 extern "C" LLVMMetadataRef LLVMRustDIBuilderCreateFile(