These tests will be failing on many platforms until #8465 is resolved.
Luckily, the particular function signature used for __divXc3 and __mulXc3
seems to be OK on x86-64.
According to https://github.com/WebAssembly/tool-conventions/blob/main/BasicCABI.md
the size of c's long double is 16 bytes for Wasm, rather than 8 bytes
which was the value previously in the compiler. This ensures
we not only pass the correct value, but also creates the correct
function signature needed to pass the Wasm validator.
This also adds an additional test case in c_abi tests.
