using symlinks in rustdoc-js tests static.files to bypass minification causes writes through symlinks, minifying orignal files

[lolbinarycat]

with the removal of --disable-minification, i was under the impression that the reccommended workflow is to symlink files in the static.files directory to their origin locations.

this workaround works completly fine when used on regular docs, however, it causes serious problems when trying to use it for the static.files in the rustdoc-js dirs.

reproduction steps:

1. rm -r build/host/test/rustdoc-js
2. ./x test --stage 1 tests/rustdoc-js/type-parameters.rs (any unit test should work)
3. ln -f src/librustdoc/html/static/js/search.js build/host/test/rustdoc-js/type-parameters/static.files/search-*.js
4. ./x test --stage 1 tests/rustdoc-js/type-parameters.rs (again)

this will result in src/librustdoc/html/static/js/search.js becoming minified.

personally i think we should just bring back the --disable-minification option as perma-unstable. that or we should have a canonical implementation of this symlink hack integrated into bootstrap.