[clangd] Add --query-driver flag to clangd-indexer

When using `clangd` for cross-compiled projects, it's necessary to use the `--query-driver` flag so that `clangd` can extract the compiler's built-in header paths. However, there's no such flag for `clangd-indexer` so we're unable to build a working static index for these projects.

This patch adds a `--query-driver` flag to `clangd-indexer` for this scenario.

I saw some tests under `clang-tools-extra/clangd/test/` but I think the cross-compilation case is a bit more complex to test. Let me know if you'd like me to look into this further.

Resolves: clangd/clangd#1717

Reviewed By: nridge

Differential Revision: https://reviews.llvm.org/D157990

clang-tools-extra/clangd/indexer/IndexerMain.cpp

@@ -38,6 +38,16 @@ static llvm::cl::opt<IndexFileFormat>
                                        "binary RIFF format")),
            llvm::cl::init(IndexFileFormat::RIFF));
 
+static llvm::cl::list<std::string> QueryDriverGlobs{
+    "query-driver",
+    llvm::cl::desc(
+        "Comma separated list of globs for white-listing gcc-compatible "
+        "drivers that are safe to execute. Drivers matching any of these globs "
+        "will be used to extract system includes. e.g. "
+        "/usr/bin/**/clang-*,/path/to/repo/**/g++-*"),
+    llvm::cl::CommaSeparated,
+};
+
 class IndexActionFactory : public tooling::FrontendActionFactory {
 public:
   IndexActionFactory(IndexFileIn &Result) : Result(Result) {}
@@ -144,12 +154,16 @@ int main(int argc, const char **argv) {
 
   // Collect symbols found in each translation unit, merging as we go.
   clang::clangd::IndexFileIn Data;
+  auto Mangler = std::make_shared<clang::clangd::CommandMangler>(
+      clang::clangd::CommandMangler::detect());
+  Mangler->SystemIncludeExtractor = clang::clangd::getSystemIncludeExtractor(
+      static_cast<llvm::ArrayRef<std::string>>(
+          clang::clangd::QueryDriverGlobs));
   auto Err = Executor->get()->execute(
       std::make_unique<clang::clangd::IndexActionFactory>(Data),
       clang::tooling::ArgumentsAdjuster(
-          [Mangler = std::make_shared<clang::clangd::CommandMangler>(
-               clang::clangd::CommandMangler::detect())](
-              const std::vector<std::string> &Args, llvm::StringRef File) {
+          [Mangler = std::move(Mangler)](const std::vector<std::string> &Args,
+                                         llvm::StringRef File) {
             clang::tooling::CompileCommand Cmd;
             Cmd.CommandLine = Args;
             Mangler->operator()(Cmd, File);