[lld-macho] Add error handling for malformed TBD files

[int3]

Summary

Previously, lld would crash while complaining that `Expected<T>
must be checked before access or destruction`.

[compnerd]

Good idea

lld/MachO/Driver.cpp

static void addFile(StringRef path) {
   }
   case file_magic::macho_object:
     inputFiles.push_back(make<ObjFile>(mbref));
     break;
   case file_magic::macho_dynamically_linked_shared_lib:
     inputFiles.push_back(make<DylibFile>(mbref));
     break;
   case file_magic::tapi_file: {
-    llvm::Expected<std::unique_ptr<llvm::MachO::InterfaceFile>> result =
-        TextAPIReader::get(mbref);
-    if (!result)
+    Expected<std::unique_ptr<InterfaceFile>> result = TextAPIReader::get(mbref);
+    if (!result) {
+      error("could not load TAPI file at " + mbref.getBufferIdentifier() +
+            ": " + toString(result.takeError()));
       return;
-
+    }
     inputFiles.push_back(make<DylibFile>(**result));
     break;
   }
   default:
     error(path + ": unhandled file type");
   }
 }
 

lld/test/MachO/invalid/invalid-stub.s

+# REQUIRES: x86
+# RUN: mkdir -p %t
+# RUN: echo "--- !tapi-tbd-v3" > %t/libinvalidYAML.tbd
+# RUN: echo "invalid YAML" >> %t/libinvalidYAML.tbd
+# RUN: llvm-mc -filetype obj -triple x86_64-apple-darwin %s -o %t/test.o
+# RUN: not lld -flavor darwinnew -Z -L%t -linvalidYAML %t/test.o -o %t/test -Z 2>&1 | FileCheck %s -DDIR=%t
+
+# CHECK: could not load TAPI file at [[DIR]]/libinvalidYAML.tbd: malformed file
+
+.globl _main
+_main:
+  ret