[clang] Always allow including builtin headers in [no_undeclared_headers] modules.

Previously, this would fail if the builtin headers had been "claimed" by
a different module that wraps these builtin headers. libc++ does this,
for example.

This change adds a test demonstrating this situation; the test fails
without the fix.

1 files changed, 6 insertions, 2 deletions

diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
index 85bf93a..bcdc5b8 100644
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -387,13 +387,17 @@ bool ModuleMap::isBuiltinHeader(StringRef FileName) {
            .Default(false);
 }
 
+bool ModuleMap::isBuiltinHeader(const FileEntry *File) {
+  return File->getDir() == BuiltinIncludeDir &&
+         ModuleMap::isBuiltinHeader(llvm::sys::path::filename(File->getName()));
+}
+
 ModuleMap::HeadersMap::iterator
 ModuleMap::findKnownHeader(const FileEntry *File) {
   resolveHeaderDirectives(File);
   HeadersMap::iterator Known = Headers.find(File);
   if (HeaderInfo.getHeaderSearchOpts().ImplicitModuleMaps &&
-      Known == Headers.end() && File->getDir() == BuiltinIncludeDir &&
-      ModuleMap::isBuiltinHeader(llvm::sys::path::filename(File->getName()))) {
+      Known == Headers.end() && ModuleMap::isBuiltinHeader(File)) {
     HeaderInfo.loadTopLevelSystemModules();
     return Headers.find(File);
   }