COFF: Fix a bug of __imp_ symbol.

The change I made in r240620 was not correct. If a symbol foo is
defined, and if you use __imp_foo, __imp_foo symbol is automatically
defined as a pointer (not just an alias) to foo.

Now that we need to create a chunk for automatically-created symbols.
I defined LocalImportChunk class for them.

llvm-svn: 240622
diff --git a/lld/COFF/Chunks.cpp b/lld/COFF/Chunks.cpp
index 527ad3b..95626fd 100644
--- a/lld/COFF/Chunks.cpp
+++ b/lld/COFF/Chunks.cpp
@@ -253,6 +253,10 @@
   }
 }
 
+void LocalImportChunk::writeTo(uint8_t *Buf) {
+  write32le(Buf + FileOff, Sym->getRVA());
+}
+
 void BaserelChunk::writeTo(uint8_t *Buf) {
   memcpy(Buf + FileOff, Data.data(), Data.size());
 }