[WebAssembly] Covert llvm/test/MC/WebAssembly/reloc-code.ll to asm. NFC

Also increase coverage of call_indirect via explict function table
(enabled when reference types is enabled) in
llvm/test/CodeGen/WebAssembly/call-indirect.ll (I believe this
was an oversight that it was not added in https://reviews.llvm.org/D90948)

Differential Revision: https://reviews.llvm.org/D120521