Set --sysroot

Author: Vinh Tran

rust/private/rustc.bzl

@@ -1039,7 +1039,7 @@ def construct_arguments(
         ))
 
     # Ensure the sysroot is set for the target platform
-    env["SYSROOT"] = toolchain.sysroot
+    rustc_flags.add("--sysroot=" + toolchain.sysroot)
 
     if toolchain._rename_first_party_crates:
         env["RULES_RUST_THIRD_PARTY_DIR"] = toolchain._third_party_dir