[WebAssembly] Only call llvm::value::dump() in debug build.

This fixes compile error in r336759. llvm::value::dump is not available
in released build.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336770 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed