Use rules_rust extra_rustc_flag instead of RUSTFLAGS for linker fix.

RUSTFLAGS is a Cargo convention not read by rustc directly. Use the
rules_rust setting which injects the flag into the actual rustc
command line, including for the bootstrap process_wrapper.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sayrer

.bazelrc

@@ -29,7 +29,7 @@ build:ci-linux --extra_execution_platforms=//tools:linux_remote
 build:ci-linux --host_platform=//tools:linux_remote
 build:ci-linux --jobs=50
 # Rust 1.86+ defaults to rust-lld on linux-x86_64; disable for remote execution
-build:ci-linux --action_env=RUSTFLAGS=-Clink-self-contained=no
+build:ci-linux --@rules_rust//rust/settings:extra_rustc_flag=-Clink-self-contained=no
 build:ci-linux --remote_executor=grpcs://remote.buildbuddy.io
 build:ci-linux --remote_default_exec_properties=container-image=docker://ghcr.io/sayrer/twitter-text-build@sha256:5af27112f67cf17164eb8f762328df9777faf026bf80aa3c8002282eb0aa95a9