[tools] add -help option for opt.

[python3kgae]

Add -help option to opt in opt.cpp.

The -help option for opt in clean llvm3.7 was disabled with
disable -help

Fixes #5514

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff ac36a797d3470e8ee906b98457a59270d01db30d 96bde99deeaad52f6d2d1c81296e9c00fa2ae0f8 -- tools/opt/opt.cpp

View the diff from clang-format here.

diff --git a/tools/opt/opt.cpp b/tools/opt/opt.cpp
index a7e9c989..faba610d 100644
--- a/tools/opt/opt.cpp
+++ b/tools/opt/opt.cpp
@@ -387,12 +387,12 @@ int __cdecl main(int argc, char **argv) {
 
   cl::ParseCommandLineOptions(argc, argv,
     "llvm .bc -> .bc modular optimizer and analysis printer\n");
-// HLSL Change Starts: add help option.
+  // HLSL Change Starts: add help option.
   if (Help) {
-      cl::PrintHelpMessage();
-      return 2;
+    cl::PrintHelpMessage();
+    return 2;
   }
-// HLSL Change Ends
+  // HLSL Change Ends
 
   if (AnalyzeOnly && NoOutput) {
     errs() << argv[0] << ": analyze mode conflicts with no-output mode.\n";

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