[WebAssembly] Combine emscripten SjLj tests

Summary:
Combine a test in lower-em-sjlj-longjmp-only.ll into lower-em-sjlj.ll,
because the test command is the same and I don't see any reason it
should be a separate file. Also converted tabs into spaces and fixed
indentations in lower-em-sjlj-sret.ll. (lower-em-sjlj.ll uses a
different test command (llc), so it couldn't be combined)

Reviewers: dschuff

Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66728

llvm-svn: 369974