[WebAssembly] objdump: Don't assume all relocations have symbols

Subscribers: jfb, dschuff, jgravelle-google, aheejin, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D46134

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330959 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed