std: merge sys::pal::common and sys_common into sys::helpers

[joboet]

As per #117276, this removes sys_common and moves its functionality and that of sys::pal::common into a newly created sys::helpers module.

[rustbot]

r? @Mark-Simulacrum

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[rust-log-analyzer]

The job x86_64-gnu-miri failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

tests/fail/tree_borrows/wildcard/subtree_internal_relatedness.rs ... ok
tests/fail/tree_borrows/wildcard/subtree_internal_relatedness_wildcard.rs ... ok

FAILED TEST: tests/fail/shims/fs/isolated_file.rs
command: MIRI_ENV_VAR_TEST="0" MIRI_TEMP="/tmp/miri-uitest-8GMQFD" RUST_BACKTRACE="1" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/miri" "--error-format=json" "--sysroot=/checkout/obj/build/x86_64-unknown-linux-gnu/miri-sysroot" "-Dwarnings" "-Dunused" "-Ainternal_features" "-Zui-testing" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/tmp/miri_ui/0/tests/fail/shims/fs" "tests/fail/shims/fs/isolated_file.rs" "--edition" "2021"

error: actual output differed from expected
Execute `./miri test --bless` to update `tests/fail/shims/fs/isolated_file.stderr` to the actual output
--- tests/fail/shims/fs/isolated_file.stderr
+++ <stderr output>
---
   = help: set `MIRIFLAGS=-Zmiri-disable-isolation` to disable isolation;
   = help: or set `MIRIFLAGS=-Zmiri-isolation-error=warn` to make Miri return an error code from isolated operations (if supported for that operation) and continue with a warning
   = note: BACKTRACE:
   = note: inside closure at /checkout/library/std/src/sys/fs/unix.rs:1229:36: 1229:84
   = note: inside `std::sys::pal::unix::cvt_r::<i32, {closure@std::sys::fs::unix::File::open_c::{closure#0}}>` at /checkout/library/std/src/sys/pal/unix/mod.rs:312:19: 312:22
   = note: inside `std::sys::fs::unix::File::open_c` at /checkout/library/std/src/sys/fs/unix.rs:1229:18: 1229:87
   = note: inside closure at /checkout/library/std/src/sys/fs/unix.rs:1217:42: 1217:66
   = note: inside `std::sys::helpers::small_c_string::run_with_cstr_stack::<std::sys::fs::unix::File>` at /checkout/library/std/src/sys/helpers/small_c_string.rs:48:18: 48:22
   = note: inside `std::sys::helpers::small_c_string::run_with_cstr::<std::sys::fs::unix::File>` at /checkout/library/std/src/sys/helpers/small_c_string.rs:28:18: 28:47
   = note: inside `std::sys::helpers::small_c_string::run_path_with_cstr::<std::sys::fs::unix::File>` at /checkout/library/std/src/sys/helpers/small_c_string.rs:18:5: 18:58
---
   = help: set `MIRIFLAGS=-Zmiri-disable-isolation` to disable isolation;
   = help: or set `MIRIFLAGS=-Zmiri-isolation-error=warn` to make Miri return an error code from isolated operations (if supported for that operation) and continue with a warning
   = note: BACKTRACE:
   = note: inside closure at /checkout/library/std/src/sys/fs/unix.rs:1229:36: 1229:84
   = note: inside `std::sys::pal::unix::cvt_r::<i32, {closure@std::sys::fs::unix::File::open_c::{closure#0}}>` at /checkout/library/std/src/sys/pal/unix/mod.rs:312:19: 312:22
   = note: inside `std::sys::fs::unix::File::open_c` at /checkout/library/std/src/sys/fs/unix.rs:1229:18: 1229:87
   = note: inside closure at /checkout/library/std/src/sys/fs/unix.rs:1217:42: 1217:66
   = note: inside `std::sys::helpers::small_c_string::run_with_cstr_stack::<std::sys::fs::unix::File>` at /checkout/library/std/src/sys/helpers/small_c_string.rs:48:18: 48:22
   = note: inside `std::sys::helpers::small_c_string::run_with_cstr::<std::sys::fs::unix::File>` at /checkout/library/std/src/sys/helpers/small_c_string.rs:28:18: 28:47
   = note: inside `std::sys::helpers::small_c_string::run_path_with_cstr::<std::sys::fs::unix::File>` at /checkout/library/std/src/sys/helpers/small_c_string.rs:18:5: 18:58
---
Location:
   /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ui_test-0.30.3/src/lib.rs:365

  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ BACKTRACE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
   1: <color_eyre[e7c328141dc6e792]::config::EyreHook>::into_eyre_hook::{closure#0}<unknown>
      at <unknown source file>:<unknown line>
   2: <eyre[c6b6b66cf346b0db]::Report>::from_adhoc::<&str><unknown>
      at <unknown source file>:<unknown line>
   3: ui_test[244b168814d5c9f]::run_tests_generic::<ui_test[244b168814d5c9f]::default_file_filter, ui[7f45f5ee1ee56943]::run_tests::{closure#1}, alloc[4ec70012adc5d5b5]::boxed::Box<dyn ui_test[244b168814d5c9f]::status_emitter::StatusEmitter>><unknown>
      at <unknown source file>:<unknown line>
   4: ui[7f45f5ee1ee56943]::ui<unknown>
      at <unknown source file>:<unknown line>
   5: ui[7f45f5ee1ee56943]::main<unknown>
      at <unknown source file>:<unknown line>
   6: std[9497a7cd472c07e6]::sys::backtrace::__rust_begin_short_backtrace::<fn() -> core[310020f84da4c26f]::result::Result<(), eyre[c6b6b66cf346b0db]::Report>, core[310020f84da4c26f]::result::Result<(), eyre[c6b6b66cf346b0db]::Report>><unknown>
      at <unknown source file>:<unknown line>
   7: std[9497a7cd472c07e6]::rt::lang_start::<core[310020f84da4c26f]::result::Result<(), eyre[c6b6b66cf346b0db]::Report>>::{closure#0}<unknown>
      at <unknown source file>:<unknown line>
   8: std[9497a7cd472c07e6]::rt::lang_start_internal<unknown>
      at <unknown source file>:<unknown line>
   9: main<unknown>
      at <unknown source file>:<unknown line>
  10: __libc_start_main<unknown>
      at <unknown source file>:<unknown line>
  11: _start<unknown>
      at <unknown source file>:<unknown line>

Run with COLORBT_SHOW_HIDDEN=1 environment variable to disable frame filtering.
Run with RUST_BACKTRACE=full to include source snippets.
error: test failed, to rerun pass `--test ui`

Caused by:
  process didn't exit successfully: `/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/deps/ui-a516ba818a7622d0` (exit status: 1)
Bootstrap failed while executing `test --stage 2 src/tools/miri src/tools/miri/cargo-miri`
Command `/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo test --target x86_64-unknown-linux-gnu -Zbinary-dep-depinfo -j 4 -Zroot-dir=/checkout --locked --color=always --release --manifest-path /checkout/src/tools/miri/Cargo.toml -- [workdir=/checkout]` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/tool.rs:191:21
Executed at: src/bootstrap/src/core/build_steps/test.rs:733:19

Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:47:45
  local time: Tue Dec 16 06:51:59 UTC 2025
  network time: Tue, 16 Dec 2025 06:51:59 GMT
##[error]Process completed with exit code 1.
##[group]Run echo "disk usage:"

[fbstj]

Suggested change

	// Computes (value*numerator)/denom without overflow, as long as both (numerator*denom) and the
	// overall result fit into i64 (which is the case for our time conversions).
	/// Computes (value*numerator)/denom without overflow, as long as both (numerator*denom) and the
	/// overall result fit into i64 (which is the case for our time conversions).

?