Fix memory leak.

Symbol's dtors are not called because they are allocated using
BumpPtrAllocators. So, members of std::unique_ptr type are not
freed when symbols are deallocated.

This patch is to allocate Thunks using BumpPtrAllocators.

llvm-svn: 274896
diff --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
index 3495da4..de38fc4 100644
--- a/lld/ELF/InputFiles.cpp
+++ b/lld/ELF/InputFiles.cpp
@@ -353,8 +353,9 @@
   InputSectionBase<ELFT> *Sec = getSection(*Sym);
   if (Binding == STB_LOCAL) {
     if (Sym->st_shndx == SHN_UNDEF)
-      return new (Alloc) Undefined(Sym->st_name, Sym->st_other, Sym->getType());
-    return new (Alloc) DefinedRegular<ELFT>(*Sym, Sec);
+      return new (this->Alloc)
+          Undefined(Sym->st_name, Sym->st_other, Sym->getType());
+    return new (this->Alloc) DefinedRegular<ELFT>(*Sym, Sec);
   }
 
   StringRef Name = check(Sym->getName(this->StringTable));