Add the rust std as a custom sysroot

library/std/riscv64.json

@@ -0,0 +1,22 @@
+{
+    "llvm-target": "riscv64",
+    "llvm-abiname": "lp64",
+    "abi": "lp64",
+    "data-layout": "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128",
+    "target-endian": "little",
+    "target-pointer-width": 64,
+    "arch": "riscv64",
+    "os": "survos",
+    "vendor": "unknown",
+    "env": "",
+    "features": "+i,+m,+a,+zicsr",
+    "linker": "ld.lld",
+    "linker-flavor": "ld",
+    "executables": true,
+    "panic-strategy": "abort",
+    "relocation-model": "static",
+    "disable-redzone": true,
+    "emit-debug-gdb-scripts": false,
+    "eh-frame-header": false,
+    "code-model": "medium"
+}