[ELF] clang-format ReaderELF.cpp

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@172674 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Use operator new(std::size_t, BumpPtrAllocator).

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@172675 91177308-0d34-0410-b5e6-96231b3b80d8