stdbuf: cargo check fails on NetBSD

[oech3]

error: failed to run custom build command for `uu_stdbuf v0.7.0 (/project/src/uu/stdbuf)`

Caused by:
  process didn't exit successfully: `/target/debug/build/uu_stdbuf-b8ce05bc7430ef3d/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-changed=build.rs
  cargo:rerun-if-changed=src/libstdbuf/src/libstdbuf.rs

  --- stderr
     Compiling dtor-proc-macro v0.0.6
     Compiling libc v0.2.182
     Compiling dtor v0.1.1
     Compiling uu_stdbuf_libstdbuf v0.7.0 (/project/src/uu/stdbuf/src/libstdbuf)
     Compiling ctor-proc-macro v0.0.7
     Compiling ctor v0.6.3
  error: linking with `x86_64-unknown-netbsd-gcc` failed: exit status: 1
    |
    = note:  "x86_64-unknown-netbsd-gcc" "-Wl,--version-script=/tmp<sysroot>chYXj1S/list" "-Wl,--no-undefined-version" "-m64" "/tmp<sysroot>chYXj1S/symbols.o" "<2 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "/target/x86_64-unknown-netbsd/debug/build/uu_stdbuf-e8aa1c89f112c985/out/libstdbuf-build/x86_64-unknown-netbsd/debug/deps/{liblibc-baeae2a85fdcd41c.rlib,libctor-bc6d4b009157f996.rlib,libdtor-41ceaa306471940e.rlib}.rlib" "<sysroot>/lib/rustlib/x86_64-unknown-netbsd/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,libcfg_if-*,liblibc-*,liballoc-*,librustc_std_workspace_core-*,libcore-*,libcompiler_builtins-*}.rlib" "-Wl,-Bdynamic" "-lutil" "-lrt" "-lutil" "-lexecinfo" "-lpthread" "-lrt" "-lgcc_s" "-lc" "-lm" "-lrt" "-lpthread" "-lutil" "-lrt" "-lutil" "-lexecinfo" "-L" "/tmp<sysroot>chYXj1S/raw-dylibs" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-o" "/target/x86_64-unknown-netbsd/debug/build/uu_stdbuf-e8aa1c89f112c985/out/libstdbuf-build/x86_64-unknown-netbsd/debug/deps/libstdbuf.so" "-Wl,--gc-sections" "-shared" "-Wl,-z,relro,-z,now" "-fPIC" "-z" "defs"
    = note: some arguments are omitted. use `--verbose` to show all linker arguments
    = note: /usr/local/lib/gcc/x86_64-unknown-netbsd/9.4.0/../../../../x86_64-unknown-netbsd/bin/ld: cannot find -lexecinfo
            collect2: error: ld returned 1 exit status
            

  error: could not compile `uu_stdbuf_libstdbuf` (lib) due to 1 previous error

  thread 'main' panicked at src/uu/stdbuf/build.rs:108:5:
  Failed to build libstdbuf
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish...
Error: Process completed with exit code 101.

[0323pin]

@oech3 This might require a bit more work. Because, stdin, stdout, and stderr are undefined references when linking libstdbuf.so as a shared library on NetBSD. On Linux and other platforms these are exported symbols from libc, but on NetBSD they are macros rather than exported symbols, so the linker can't find them.