Rollup merge of #143964 - nikic:docker-script-arg, r=marcoieni

Fix handling of SCRIPT_ARG in docker images

Instead of making this a build parameter, pass the SCRIPT as an environment variable.

To this purpose, normalize on always referring to a script in `/scripts`.

For i686-gnu-nopt-2 I had to create a separate script, because Docker seems to be really terrible at command line argument parsing, so it's not possible to pass an environment variable that contains whitespace.

Fixes rust-lang/rust#143962.

try-job: `dist-x86_64-linux`
try-job: `i686-gnu-nopt-*`
try-job: `i686-gnu-*`
try-job: `x86_64-gnu-llvm-19-*`
try-job: `x86_64-gnu-llvm-20-*`

Author: fmease