Most lit/help tests fail with new python-filecheck

[rathann]

In binaryen lit tests, filecheck is used to test the --help output of various wasm* tools.

With filecheck-0.0.24, the following test passes:

$ wasm-shell --help | filecheck help/wasm-shell.test
$ 

However, with filecheck-1.0.3 from the new upstream repo, it fails:

$ wasm-shell --help | filecheck help/wasm-shell.test
help/wasm-shell.test:4:9 found empty check string with prefix 'NEXT:'
;; CHECK-NEXT:
        ^
$

New upstream says the new behaviour is closer to the original filecheck and recommends using CHECK-EMPTY instead of CHECK-NEXT.