Use a forward declaration. NFC.

llvm-svn: 303363
diff --git a/lld/ELF/MapFile.cpp b/lld/ELF/MapFile.cpp
index 23c63e8..c3f4f5a 100644
--- a/lld/ELF/MapFile.cpp
+++ b/lld/ELF/MapFile.cpp
@@ -21,6 +21,7 @@
 
 #include "MapFile.h"
 #include "InputFiles.h"
+#include "OutputSections.h"
 #include "Strings.h"
 #include "SymbolTable.h"
 #include "Threads.h"
diff --git a/lld/ELF/MapFile.h b/lld/ELF/MapFile.h
index 24d6368..89d4d2d 100644
--- a/lld/ELF/MapFile.h
+++ b/lld/ELF/MapFile.h
@@ -10,10 +10,11 @@
 #ifndef LLD_ELF_MAPFILE_H
 #define LLD_ELF_MAPFILE_H
 
-#include "OutputSections.h"
+#include <llvm/ADT/ArrayRef.h>
 
 namespace lld {
 namespace elf {
+class OutputSection;
 template <class ELFT>
 void writeMapFile(llvm::ArrayRef<OutputSection *> OutputSections);
 }