fix target json

Author: RalfJung

src/tools/miri/tests/x86_64-unknown-kernel.json

@@ -2,7 +2,7 @@
   "llvm-target": "x86_64-unknown-none",
   "target-endian": "little",
   "target-pointer-width": "64",
-  "target-c-int-width": "32",
+  "target-c-int-width": 32,
   "data-layout": "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128",
   "arch": "x86_64",
   "os": "none",