bootstrap failed when enable both 'gcc'/'llvm' codegen backends

Summary

when i bootstrap main rustc, it failed with

thread 'main' (83973) panicked at src/bootstrap/src/core/build_steps/compile.rs:1623:34:
libgccjit_path.canonicalize() failed with No such file or directory (os error 2) ("Cannot find libgccjit at /home/zhanghe/rust/build/x86_64-unknown-linux-gnu/gcc/x86_64-unknown-linux-gnu/install/lib/libgccjit.so"

Command used

zhanghe@zhanghe-System-Product-Name:~/rust$ export DESTDIR=/home/zhanghe/rustgccjit
zhanghe@zhanghe-System-Product-Name:~/rust$ ./x install --config config.example.toml

Expected behaviour

Actual behaviour

Bootstrap configuration (bootstrap.toml)

change-id = 148671
[build]
docs = false
extended = true
optimized-compiler-builtins = true
tools = [
    "cargo",
    "clippy",
    "rustfmt",
    "rust-analyzer",
    "rust-analyzer-proc-macro-srv",
    "analysis",
    "src",
    "wasm-component-ld",
    "miri", "cargo-miri" # for dev/nightly channels
]
build = "x86_64-unknown-linux-gnu"
host = ["x86_64-unknown-linux-gnu"]
target = [
    "x86_64-unknown-linux-gnu",
    ]

[target."x86_64-unknown-linux-gnu"]
profiler = true

[llvm]
download-ci-llvm = false
[gcc]
download-ci-gcc = false

[rust]
codegen-backends = ["llvm","gcc"]
download-rustc = false

[dist]
compression-formats = ["xz"]
vendor = false

Operating system

HEAD

Additional context

<log>

Reproduce the failure with ./x install --config config.example.toml using both codegen-backends = ["llvm", "gcc"] and the provided bootstrap settings. Start at src/bootstrap/src/core/build_steps/compile.rs:1623, then trace how the configured GCC backend path is produced. Done means the bootstrap completes without the libgccjit.so missing-file panic.