SourceKit: handle Windows paths for request options

Windows paths involve a `:`.  Ideally, we would just use `;` as the
separator rather than `:`, but for now special case a single character
entry as a drive letter.

Author: compnerd

tools/SourceKit/tools/sourcekitd-test/sourcekitd-test.cpp

@@ -430,14 +430,20 @@ static bool setSyntacticMacroExpansions(sourcekitd_object_t req,
     StringRef(opt).split(args, ":");
     unsigned line, column;
 
-    if (args.size() != 3 || args[0].getAsInteger(10, line) ||
+    if ((args.size() != 3 && !(args.size() == 4 || args[3].size() == 1)) ||
+        args[0].getAsInteger(10, line) ||
         args[1].getAsInteger(10, column)) {
       llvm::errs() << "-req-opts should be {line}:{column}:{json-path}";
       return true;
     }
     unsigned offset = resolveFromLineCol(line, column, inputBuf);
 
-    auto Buffer = getBufferForFilename(args[2], opts.VFSFiles)->getBuffer();
+    std::string path;
+    if (args.size() == 3)
+      path = args[2];
+    else
+      path = (args[2] + Twine(":") + args[3]).str();
+    auto Buffer = getBufferForFilename(path, opts.VFSFiles)->getBuffer();
     char *Err = nullptr;
     auto expansion = sourcekitd_request_create_from_yaml(Buffer.data(), &Err);
     if (!expansion) {