Allow vscr to be marked as a clobber in PowerPC inline asm

[pmur]

I don't think gcc or llvm do anything with vscr, but they do allow it to be marked as a clobber. This prevents needing to enumerate it as a preserved flag if an update does make use of it.

ELFv2 defines this as a "limited-access" register. This means the VSCR[SAT] bit is clobbered by a function call.

r? @Amanieu

[rustbot]

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

[rust-log-analyzer]

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spellchecking files
building external tool typos from package typos-cli@1.38.1
finished building tool typos
npm WARN deprecated puppeteer@22.15.0: < 24.10.2 is no longer supported
npm ERR! code 127
npm ERR! git dep preparation failed
npm ERR! command /node/bin/node /node/lib/node_modules/npm/bin/npm-cli.js install --force --cache=/home/user/.npm --prefer-offline=false --prefer-online=false --offline=false --no-progress --no-save --no-audit --include=dev --include=peer --include=optional --no-package-lock-only --no-dry-run
npm ERR! npm WARN using --force Recommended protections disabled.
npm ERR! npm WARN deprecated inflight@1.0.6: This module is not supported, and leaks memory. Do not use it. Check out lru-cache if you want a good and tested way to coalesce async requests by a key value, which is much more comprehensive and powerful.
npm ERR! npm WARN deprecated glob@7.2.3: Glob versions prior to v9 are no longer supported
npm ERR! npm WARN deprecated glob@7.2.3: Glob versions prior to v9 are no longer supported
npm ERR! npm WARN deprecated readdir-scoped-modules@1.1.0: This functionality has been moved to @npmcli/fs
npm ERR! npm WARN deprecated debuglog@1.0.1: Package no longer supported. Contact Support at https://www.npmjs.com/support for more info.
npm ERR! npm WARN deprecated read-package-json@2.1.2: This package is no longer supported. Please use @npmcli/package-json instead.
npm ERR! npm WARN deprecated read-installed@4.0.3: This package is no longer supported.
npm ERR! npm ERR! code 127
npm ERR! npm ERR! path /home/user/.npm/_cacache/tmp/git-cloneXXXXXXDVR1XF/node_modules/rollup
npm ERR! npm ERR! command failed
npm ERR! npm ERR! command sh -c patch-package
npm ERR! npm ERR! sh: 1: patch-package: not found
npm ERR! 
npm ERR! npm ERR! A complete log of this run can be found in: /home/user/.npm/_logs/2025-11-07T18_10_00_257Z-debug-0.log

npm ERR! A complete log of this run can be found in: /home/user/.npm/_logs/2025-11-07T18_09_52_993Z-debug-0.log
npm install did not exit successfully
tidy [extra_checks]: IO error: npm install returned exit code exit status: 127
tidy [extra_checks]: FAIL
tidy: The following check failed: extra_checks
Bootstrap failed while executing `test src/tools/tidy tidyselftest --extra-checks=py,cpp,js,spellcheck`
Command `/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools-bin/rust-tidy /checkout /checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo /checkout/obj/build 4 /node/bin/npm --extra-checks=py,cpp,js,spellcheck` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/tool.rs:1549:23
Executed at: src/bootstrap/src/core/build_steps/test.rs:1279:29

Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:02:58
  local time: Fri Nov  7 18:10:18 UTC 2025
  network time: Fri, 07 Nov 2025 18:10:18 GMT
##[error]Process completed with exit code 1.
##[group]Run echo "disk usage:"