[WebAssembly] Improve error messages regarding missing indirect function table. NFC

[sbc100]

Summary

Use report_fatal_error here since this is an internal error, and not
something the user can/should be trying to fix.

Also distinguish between the symbol being missing and the symbol having
the wrong type.

We have a failure internally where the symbol is missing. Currently
trying to reduce the test case to something we can attach to an llvm
bug.

[sbc100]

typo

llvm/lib/MC/WasmObjectWriter.cpp

if (Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB ||
       Type == wasm::R_WASM_TABLE_INDEX_SLEB ||
       Type == wasm::R_WASM_TABLE_INDEX_SLEB64 ||
       Type == wasm::R_WASM_TABLE_INDEX_I32 ||
       Type == wasm::R_WASM_TABLE_INDEX_I64) {
     // TABLE_INDEX relocs implicitly use the default indirect function table.
     // We require the function table to have already been defined.
     auto TableName = "__indirect_function_table";
     MCSymbolWasm *Sym = cast_or_null<MCSymbolWasm>(Ctx.lookupSymbol(TableName));
-    if (!Sym || !Sym->isFunctionTable()) {
-      Ctx.reportError(
-          Fixup.getLoc(),
-          "symbol '__indirect_function_table' is not a function table");
+    if (!Sym) {
+      report_fatal_error("missing indirect function table symbol");
     } else {
+      if (!Sym->isFunctionTable())
+        report_fatal_error("__indirect_function_table symbol has wrong type");
       // Ensure that __indirect_function_table reaches the output.
       Sym->setNoStrip();
       Asm.registerSymbol(*Sym);
     }
   }
 
   // Relocation other than R_WASM_TYPE_INDEX_LEB are required to be
   // against a named symbol.