[WebAssembly] Refactor WasmObjectWriter::writeObject

The size of this function was getting a little out of.
control.  Split code for writing each section type into
seperate functions.

Differential Revision: https://reviews.llvm.org/D33792

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304634 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed