[lld][WebAssembly] update error to continue for R_WASM_FUNCTION_INDEX_I32 (#162403)

with some builds we're getting `[libcxx/include/optional:874](libcxx/include/optional): libc++ Hardening assertion this->has_value() failed: optional operator* called on a disengaged value` since error() adds the errmsg into the stream and continues, but given it's an unsupported relocation type it eventually crashes. Given that I see that we're already using Fatal() in some of the other places where it hits unsupported relocation type, my uneducated guess is that this should be fine.

Author: kevinwkt

lld/wasm/InputChunks.cpp

@@ -439,9 +439,11 @@ bool InputChunk::generateRelocationCode(raw_ostream &os) const {
  if (!requiresRuntimeReloc)
  continue;
 
- if (!isValidRuntimeRelocation(rel.getType()))
+ if (!isValidRuntimeRelocation(rel.getType())) {
  error("invalid runtime relocation type in data section: " +
  relocTypetoString(rel.Type));
+ continue;
+ }
 
  uint64_t offset = getVA(rel.Offset) - getInputSectionOffset();
  LLVM_DEBUG(dbgs() << "gen reloc: type=" << relocTypeToString(rel.Type)