Use more relevant file system API for error handling

Address issue with the lit tests

Author: snarang181

clang-tools-extra/clang-doc/tool/ClangDocMain.cpp

@@ -388,11 +388,8 @@ Example usage for a project using a compile commands database:
   sortUsrToInfo(USRToInfo);
 
   // Ensure the root output directory exists.
-  if (std::error_code Err = llvm::sys::fs::create_directories(OutDirectory);
-      Err != std::error_code()) {
-    ExitOnErr(llvm::createStringError(
-        llvm::inconvertibleErrorCode(), "Failed to create directory '%s': %s",
-        OutDirectory.c_str(), Err.message().c_str()));
+  if (std::error_code Err = llvm::sys::fs::create_directories(OutDirectory)) {
+  ExitOnErr(llvm::createFileError(OutDirectory, Err));
   }
 
   // Run the generator.

clang-tools-extra/test/clang-doc/invalid-file-error.test

@@ -1,4 +1,12 @@
-// RUN: not clang-doc %S/Inputs/basic-project/src/Circle.cpp -output=/root/docs 2>&1 | FileCheck %s
+// Test: Invalid output path (%t is a file, not a directory)
+// RUN: rm -rf %t && echo "not a dir" > %t
+// RUN: not clang-doc %s -output=%t/subdir 2>&1 | FileCheck --check-prefix=BAD-OUTPUT %s
 
-// CHECK: clang-doc error: Failed to create directory
+// BAD-OUTPUT: clang-doc error:
+// BAD-OUTPUT: Not a directory
 
+//
+// Test: Invalid format option
+// RUN: not clang-doc %s -format=badformat 2>&1 | FileCheck --check-prefix=BAD-FORMAT %s
+
+// BAD-FORMAT: clang-doc: for the --format option: Cannot find option named 'badformat'!