[Driver] Suggest correctly spelled driver options

Summary:
Depends on https://reviews.llvm.org/D41732.

Utilities such as `opt`, when invoked with arguments that are very
nearly spelled correctly, suggest the correctly spelled options:

```
bin/opt -hel
opt: Unknown command line argument '-hel'.  Try: 'bin/opt -help'
opt: Did you mean '-help'?
```

Clang, on the other hand, prior to this commit, does not:

```
bin/clang -hel
clang-6.0: error: unknown argument: '-hel'
```

This commit makes use of the new libLLVMOption API from
https://reviews.llvm.org/D41732 in order to provide correct suggestions:

```
bin/clang -hel
clang-6.0: error: unknown argument: '-hel', did you mean '-help'?
```

Test Plan: `check-clang`

Reviewers: yamaguchi, v.g.vassilev, teemperor, ruiu, bruno

Reviewed By: bruno

Subscribers: bruno, jroelofs, cfe-commits

Differential Revision: https://reviews.llvm.org/D41733

llvm-svn: 321917

1 files changed, 7 insertions, 1 deletions

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 6ce719aac67..ce875fa03b9 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2757,7 +2757,13 @@ bool CompilerInvocation::CreateFromArgs(CompilerInvocation &Res,
 
   // Issue errors on unknown arguments.
   for (const Arg *A : Args.filtered(OPT_UNKNOWN)) {
-    Diags.Report(diag::err_drv_unknown_argument) << A->getAsString(Args);
+    auto ArgString = A->getAsString(Args);
+    std::string Nearest;
+    if (Opts->findNearest(ArgString, Nearest, IncludedFlagsBitmask) > 1)
+      Diags.Report(diag::err_drv_unknown_argument) << ArgString;
+    else
+      Diags.Report(diag::err_drv_unknown_argument_with_suggestion)
+          << ArgString << Nearest;
     Success = false;
   }