[WebAssembly] Add linker options to control feature checking

Summary:
Adds --check-features and --no-check-features. The default for now is
to enable the checking, but this might change in the future.

Also adds --features=foo,bar for precisely controlling the features
used in the output binary.

Depends on D59173.

Reviewers: sbc100, aheejin

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59274

llvm-svn: 356805