[WebAssembly] Make LBB markers not affected by test order

Summary:
This way we can change the order of tests or delete some of them without
affecting tests for other functions.

Reviewers: tlively

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60929

llvm-svn: 359036