[ELF] Print file:line for 'undefined section' errors

Differential revision: https://reviews.llvm.org/D27108

llvm-svn: 288019
diff --git a/lld/ELF/ScriptParser.h b/lld/ELF/ScriptParser.h
index 6c314a4..a0da48d 100644
--- a/lld/ELF/ScriptParser.h
+++ b/lld/ELF/ScriptParser.h
@@ -32,6 +32,7 @@
   void skip();
   bool consume(StringRef Tok);
   void expect(StringRef Expect);
+  std::string currentLocation();
 
   std::vector<MemoryBufferRef> MBs;
   std::vector<StringRef> Tokens;