WebAssembly: mark a few new failures

A recent change introduced this assertion failure in some corner cases.

Repro:
mkdir /s/wasm/torture-out ; time /s/wasm/waterfall/src/compile_torture_tests.py --c /s/llvm/out/bin/clang --cxx /s/llvm/out/bin/clang++ --testsuite /s/gcc/gcc/testsuite --fails /s/llvm/llvm/lib/Target/WebAssembly/known_gcc_test_failures.txt --out /s/wasm/torture-out

Or look on the wasm integration bot:
https://build.chromium.org/p/client.wasm.llvm/console

llvm-svn: 257733