Add "linker_flavor": "gcc" to target.json

This field is now required; see rust-lang/rust#40018

Author: hawkw

x86_64-unknown-intermezzos-gnu.json

@@ -3,6 +3,7 @@
 	"cpu": "x86-64",
 	"data-layout": "e-m:e-i64:64-f80:128-n8:16:32:64-S128",
 	"executables": true,
+        "linker-flavor": "gcc",
 	"llvm-target": "x86_64-unknown-none-gnu",
 	"no-compiler-rt": true,
 	"os": "intermezzos",