[WebAssembly] Don't default to ELF in the triple.

WebAssembly doesn't yet have a specified binary format, and it may not
end up being ELF, so we don't want the Triple class defaulting to ELF
for it at this time.

llvm-svn: 245254
diff --git a/llvm/lib/Support/Triple.cpp b/llvm/lib/Support/Triple.cpp
index a2a88d2..201d352 100644
--- a/llvm/lib/Support/Triple.cpp
+++ b/llvm/lib/Support/Triple.cpp
@@ -539,6 +539,11 @@
     if (T.isOSDarwin())
       return Triple::MachO;
     return Triple::ELF;
+
+  case Triple::wasm32:
+  case Triple::wasm64:
+    // Unknown for now, until an object format is specified.
+    return Triple::UnknownObjectFormat;
   }
 
   if (T.isOSDarwin())