RustWrapper: work around unification of diagnostic handlers

This lets me build against llvm/main as of March 23rd, 2021. I'm not
entirely sure this is _correct_, but it appears to be functionally
identical to what was done in LLVM: existing callsites of
setInlineAsmDiagnosticHandler were moved to SetDiagnosticHandler() on
the context object, which we already set up in both places that we
called setInlineAsmDiagnosticHandler().

Author: durin42

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -1300,9 +1300,19 @@ extern "C" LLVMTypeKind LLVMRustGetTypeKind(LLVMTypeRef Ty) {
 
 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(SMDiagnostic, LLVMSMDiagnosticRef)
 
+#if LLVM_VERSION_LT(13, 0)
+using LLVMInlineAsmDiagHandlerTy = LLVMContext::InlineAsmDiagHandlerTy;
+#else
+using LLVMInlineAsmDiagHandlerTy = void*;
+#endif
+
 extern "C" void LLVMRustSetInlineAsmDiagnosticHandler(
-    LLVMContextRef C, LLVMContext::InlineAsmDiagHandlerTy H, void *CX) {
+    LLVMContextRef C, LLVMInlineAsmDiagHandlerTy H, void *CX) {
+  // Diagnostic handlers were unified in LLVM change 5de2d189e6ad, so starting
+  // with LLVM 13 this function is gone.
+#if LLVM_VERSION_LT(13, 0)
   unwrap(C)->setInlineAsmDiagnosticHandler(H, CX);
+#endif
 }
 
 extern "C" bool LLVMRustUnpackSMDiagnostic(LLVMSMDiagnosticRef DRef,