tools-make: add mock parser for clang ld output

According to #3226, it looks like clang's LD error format has changed.
This patch adds the new format so we can parse the mocks successfully.

Apple clang version 11.0.3 (clang-1103.0.32.29)

```
checking for ANSI C header files... Undefined symbols for architecture x86_64:
  "_fromwire_amount_msat", referenced from:
      _fromwire_tlv_test_n1_tlv3 in ccj4zKdV.o
  "_fromwire_bool", referenced from:
      _fromwire_test_msg in ccj4zKdV.o
      _fromwire_test_msg_option_short_id in ccj4zKdV.o
      _fromwire_test_msg_option_one in ccj4zKdV.o
      _fromwire_test_msg_option_two in ccj4zKdV.o
  "_fromwire_test_enum", referenced from:
      _fromwire_test_msg in ccj4zKdV.o
      _fromwire_test_msg_option_short_id in ccj4zKdV.o
      _fromwire_test_msg_option_one in ccj4zKdV.o
      _fromwire_test_msg_option_two in ccj4zKdV.o
  "_fromwire_tlvs", referenced from:
      _fromwire_test_tlv1 in ccj4zKdV.o
      _fromwire_test_tlv2 in ccj4zKdV.o
      _fromwire_test_tlv3 in ccj4zKdV.o
  "_fromwire_tu32", referenced from:
      _fromwire_tlv_test_n2_tlv2 in ccj4zKdV.o
  "_fromwire_tu64", referenced from:
      _fromwire_tlv_test_n1_tlv1 in ccj4zKdV.o
      _fromwire_tlv_test_n2_tlv1 in ccj4zKdV.o
  "_fromwire_u16", referenced from:
      _fromwire_test_features in ccj4zKdV.o
      _fromwire_subtype_var_assign in ccj4zKdV.o
      _fromwire_subtype_arrays in ccj4zKdV.o
      _fromwire_tlv_test_n1_tlv4 in ccj4zKdV.o
      _fromwire_tlv_test_n3_tlv3 in ccj4zKdV.o
      _fromwire_test_msg in ccj4zKdV.o
      _fromwire_test_tlv1 in ccj4zKdV.o
      ...
  "_fromwire_u32", referenced from:
      _fromwire_tlv_test_n3_tlv3 in ccj4zKdV.o
      _fromwire_test_msg in ccj4zKdV.o
      _fromwire_test_msg_option_short_id in ccj4zKdV.o
      _fromwire_test_msg_option_one in ccj4zKdV.o
      _fromwire_test_msg_option_two in ccj4zKdV.o
  "_fromwire_u64", referenced from:
      _fromwire_test_short_id in ccj4zKdV.o
      _fromwire_tlv_test_n3_tlv3 in ccj4zKdV.o
  "_fromwire_u8", referenced from:
      _fromwire_subtype_var_assign in ccj4zKdV.o
      _fromwire_subtype_var_len in ccj4zKdV.o
      _fromwire_subtype_varlen_varsize in ccj4zKdV.o
      _fromwire_tlv_test_n3_tlv3 in ccj4zKdV.o
  "_fromwire_u8_array", referenced from:
      _fromwire_test_features in ccj4zKdV.o
      _fromwire_subtype_arrays in ccj4zKdV.o
      _fromwire_tlv_test_n3_tlv3 in ccj4zKdV.o
      _fromwire_test_msg in ccj4zKdV.o
      _fromwire_test_msg_option_short_id in ccj4zKdV.o
      _fromwire_test_msg_option_one in ccj4zKdV.o
      _fromwire_test_msg_option_two in ccj4zKdV.o
      ...
```

Changelog-Fixed: Build for macOS Catalina / Apple clang v11.0.3 fixed

tools/mockup.sh

@@ -14,6 +14,12 @@ if [ $# -eq 0 ]; then
 		# ld: error: undefined symbol: foo()
 		echo "${LINE#*undefined symbol: }"
 		;;
+	    *,\ referenced\ from:*)
+		# Apple clang version 11.0.3 (clang-1103.0.32.29)
+                # "_towire", referenced from:
+		LINE=${LINE#\"_}
+		echo "${LINE%\"*}"
+		;;
 	    *)
 		continue
 		;;