[WebAssembly] Fix p2align in assembler.
Summary:
- Match the syntax output by InstPrinter.
- Fix it always emitting 0 for align. Had to work around fact that
opcode is not available for GetDefaultP2Align while parsing.
- Updated tests that were erroneously happy with a p2align=0
Fixes https://bugs.llvm.org/show_bug.cgi?id=40752
Reviewers: aheejin, sbc100
Subscribers: jgravelle-google, sunfish, jfb, llvm-commits, dschuff
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D63633
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@364570
91177308-0d34-0410-b5e6-
96231b3b80d8