Need ability to specify optimization level or release mode for specific dependencies

[JetForMe]

Description

It is currently not possible to compile a dependency in release mode, or with optimizations turned on, without doing so for the entire project. Some dependencies are performance-sensitive, and having them run unoptimized during development can really slow things down. In my case, I'm using Whisper.cpp to transcribe speech. But another use case is plug-ins, which aren't dependencies per se, but get compiled and run frequently during development.

Here are several forum topics on the matter:

• https://forums.swift.org/t/force-package-dependencies-as-optimized-builds/76390/2
• https://forums.swift.org/t/build-swiftpm-dependencies-using-custom-build-configuration/70065
• https://forums.swift.org/t/status-of-compilation-of-dependencies-with-optimizations-in-debug-mode/77214/5

SPM needs a means of changing the build mode or specifying optimization flags for dependencies, and it needs to work whether the module is Swift or C or any other language.

Expected behavior

No response

Actual behavior

No response

Steps to reproduce

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Swift Package Manager version/commit hash

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Swift & OS version (output of swift --version && uname -a)

No response