[WebAssembly] Add validation to reloc section

We now check relocations offsets are within range, and the relocation
index is valid.

Also updated tests which contained invalid Wasm files that were
previously not checked.

Differential Revision: https://reviews.llvm.org/D43684

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@326697 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed