Revert r304117 - WebAssembly object format isn't ready to be the default

[jgravelle-google]

Summary

Wasm object format has some functionality regressions from the ELF format, and doesn't play nicely with the rest of the toolchain. It should eventually be the default, but not yet.

[sbc100]

lgtm.

lib/Support/Triple.cpp

static Triple::ObjectFormatType getDefaultFormat(const Triple &T) {
   case Triple::sparcel:
   case Triple::sparcv9:
   case Triple::spir:
   case Triple::spir64:
   case Triple::systemz:
   case Triple::tce:
   case Triple::tcele:
   case Triple::thumbeb:
-  case Triple::xcore:
-    return Triple::ELF;
-
   case Triple::wasm32:
   case Triple::wasm64:
-    return Triple::Wasm;
+  case Triple::xcore:
+    return Triple::ELF;
 
   case Triple::ppc:
   case Triple::ppc64:
     if (T.isOSDarwin())
       return Triple::MachO;
     return Triple::ELF;
   }
   llvm_unreachable("unknown architecture");