[libc] allow libc-hdrgen to work on windows files (#87292)

The code does some (overly simple?) checks on file syntax. These checks
assume unix line endings and fail on windows. This commit updates the
code to strip extra whitespace, making the checks more robust,
particularly in the presence of windows line endings.

Fixes #86023

Author: stephenneuendorffer

libc/utils/HdrGen/Generator.cpp

@@ -84,11 +84,19 @@ void Generator::generate(llvm::raw_ostream &OS, llvm::RecordKeeper &Records) {
       Line = Line.drop_front(CommandPrefixSize);
 
       P = Line.split("(");
+      // It's possible that we have windows line endings, so strip off the extra
+      // CR.
+      P.second = P.second.trim();
       if (P.second.empty() || P.second[P.second.size() - 1] != ')') {
         SrcMgr.PrintMessage(llvm::SMLoc::getFromPointer(P.second.data()),
                             llvm::SourceMgr::DK_Error,
                             "Command argument list should begin with '(' "
                             "and end with ')'.");
+        SrcMgr.PrintMessage(llvm::SMLoc::getFromPointer(P.second.data()),
+                            llvm::SourceMgr::DK_Error, P.second.data());
+        SrcMgr.PrintMessage(llvm::SMLoc::getFromPointer(P.second.data()),
+                            llvm::SourceMgr::DK_Error,
+                            std::to_string(P.second.size()));
         std::exit(1);
       }
       llvm::StringRef CommandName = P.first;