[WebAssembly] CFG sort support for exception handling

Summary:
This patch extends CFGSort pass to support exception handling. Once it
places a loop header, it does not place blocks that are not dominated by
the loop header until all the loop blocks are sorted. This patch extends
the same algorithm to exception 'catch' part, using the information
calculated by WebAssemblyExceptionInfo class.

Reviewers: dschuff, sunfish

Subscribers: sbc100, jgravelle-google, llvm-commits

Differential Revision: https://reviews.llvm.org/D46500

llvm-svn: 339172