[clangd] Handle '--' in QueryDriverDatabase

[nridge]

Summary

Fixes https://github.com/clangd/clangd/issues/1100,
a regression from D116721.

[sammccall]

Thanks so much for tracking this down!
The number of times we've had this bug :-( I wish we were using something a little more structured than array-of-strings.

clang-tools-extra/clangd/QueryDriverDatabase.cpp

 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/Regex.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include <algorithm>
+#include <iterator>
 #include <map>
 #include <string>
 #include <vector>
 
 namespace clang {
 namespace clangd {
 namespace {
 
log("System includes extractor: successfully executed {0}\n\tgot includes: "
       "\"{1}\"\n\tgot target: \"{2}\"",
       Driver, llvm::join(Info->SystemIncludes, ", "), Info->Target);
   return Info;
 }
 
 tooling::CompileCommand &
 addSystemIncludes(tooling::CompileCommand &Cmd,
                   llvm::ArrayRef<std::string> SystemIncludes) {
+  std::vector<std::string> ToAppend;
   for (llvm::StringRef Include : SystemIncludes) {
     // FIXME(kadircet): This doesn't work when we have "--driver-mode=cl"
-    Cmd.CommandLine.push_back("-isystem");
-    Cmd.CommandLine.push_back(Include.str());
+    ToAppend.push_back("-isystem");
+    ToAppend.push_back(Include.str());
+  }
+  if (!ToAppend.empty()) {
+    // Just append when `--` isn't present.
+    auto InsertAt = llvm::find(Cmd.CommandLine, "--");
+    Cmd.CommandLine.insert(InsertAt, std::make_move_iterator(ToAppend.begin()),
+                           std::make_move_iterator(ToAppend.end()));
   }
   return Cmd;
 }
 
 tooling::CompileCommand &setTarget(tooling::CompileCommand &Cmd,
                                    const std::string &Target) {
   if (!Target.empty()) {
     // We do not want to override existing target with extracted one.
     for (llvm::StringRef Arg : Cmd.CommandLine) {
       if (Arg == "-target" || Arg.startswith("--target="))
         return Cmd;
     }
-    Cmd.CommandLine.push_back("--target=" + Target);
+    // Just append when `--` isn't present.
+    auto InsertAt = llvm::find(Cmd.CommandLine, "--");
+    Cmd.CommandLine.insert(InsertAt, "--target=" + Target);
   }
   return Cmd;
 }
 
 /// Converts a glob containing only ** or * into a regex.
 std::string convertGlobToRegex(llvm::StringRef Glob) {
   std::string RegText;
   llvm::raw_string_ostream RegStream(RegText);