Rollup merge of #45624 - glaubitz:bootstrap-sparc64, r=kennytm

bootstrap: Add missing cputype matching for sparc64

Trying to configure rust natively on sparc64-unknown-linux-gnu currently fails with:

```
root@deb4g:/local_scratch/glaubitz/rust/rust# ./configure --host=sparc64-unknown-linux-gnu --enable-local-rust --local-rust-root=/usr/local
configure: processing command line
configure:
configure: build.host           := ['sparc64-unknown-linux-gnu']
configure: build.rustc          := /usr/local/bin/rustc
configure: build.cargo          := /usr/local/bin/cargo
configure: build.rustc          := /usr/local/bin/rustc
configure: build.cargo          := /usr/local/bin/cargo
configure: build.configure-args := ['--host=sparc64-unknown-linux-gnu', '--enable ...
unknown cpu type: sparc64
root@deb4g:/local_scratch/glaubitz/rust/rust#
```

This is trivially fixed by defining sparc64 as a valid cputype.