Respect the fileextension with roc build --lib --output file.extension

[ostcar]

When you call roc build --lib --output file.EXTENSION, the fileextension is changed to .so. This is as least true for linux.

The reason is this line:

roc/crates/compiler/build/src/link.rs

Line 979 in 62cc19c

output_path.set_extension("so");

This can not be changed without changes on other parts of roc. For example this code expects a filename with a .so extension on target linux and other specific fileextensions for other targets.

• See this discussion on zulip
• This old PR with other places, where a change of the filename did mater.
• This old PR that tried to fix this.