[WebAssembly] Don't do SjLj transformation when there's only setjmp

When there is a `setjmp` call in a function, we transform every callsite
of `setjmp` to record its information by calling `saveSetjmp` function,
and we also transform every callsite of a function that can longjmp to
to check if a longjmp occurred and if so jump to the corresponding
post-setjmp BB. Currently we are doing this for every function that
contains a call to `setjmp`, but if there is no other function call
within that function that can longjmp, this transformation of `setjmp`
callsite and all the preparation of `setjmpTable` in the entry of the
function are not necessary.

This checks if a setjmp-calling function has any other calls that can
longjmp, and if not, skips the function for the SjLj transformation.

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D107530