[WebAssembly] Make wasm-eh.cpp requires WebAssembly
[WebAssembly] Make wasm-eh.cpp requires WebAssembly

D67208 added a new test line to wasm-eh.cpp that invokes the LLVM
backend and this test fails on bots that don't have WebAssembly target.
This makes wasm-eh.cpp explicitly require WebAssembly so this will be
skipped on those targets.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@371711 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang