Fix target JSON (rust-lang/rust#136544)

Author: fmckeogh

brig/x86_64-unknown-brig.json

@@ -6,6 +6,7 @@
   "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",
   "disable-redzone": true,
   "features": "-mmx,-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2,+soft-float",
+  "rustc-abi": "x86-softfloat",
   "is-builtin": false,
   "dynamic-linking": true,
   "linker": "rust-lld",