Make build configuration (release/debug) configurable in SwiftPM plugin

[ole]

No description provided.

[ole]

Unfortunately, building in debug mode doesn't work. I have no idea why.

Relevant error: <unknown>:0: error: index output filenames do not match input source files

On macOS:

$ swift package --triple armv6m-none-none-eabi --toolchain /Library/Developer/Toolchains/swift-latest.xctoolchain/ --verbose link --objcopy /opt/homebrew/opt/llvm/bin/llvm-objcopy --configuration debug
…
info: [link] /Library/Developer/Toolchains/swift-latest.xctoolchain/usr/bin/clang \
    --target=armv6m-none-eabi \
    -mfloat-abi=soft \
    -march=armv6m \
    -O3 \
    -nostdlib \
    -c \
    /Users/elo/code/Raspberry-Pi-Pico/BootstrappedSwift/.build/plugins/Link/outputs/intermediates/bs2_default_padded_checksummed.s \
    -o \
    /Users/elo/code/Raspberry-Pi-Pico/BootstrappedSwift/.build/plugins/Link/outputs/intermediates/bs2_default_padded_checksummed.s.o
info: [link] Creating app executable
info: [link] Building product 'App' with config 'debug'
Building for debugging...
[0/5] Write swift-version-65E5C3A9CA389411.txt
warning: ignoring '-enable-batch-mode' because '-whole-module-optimization' was also specified
remark: Incremental compilation has been disabled: it is not compatible with whole module optimization
Apple Swift version 5.11-dev (LLVM 48dba337c6a2104, Swift 823db1fc0821481)
Target: armv6m-none-none-eabi
[2/7] Emitting module RP2040
[3/7] Compiling RP2040 GPIO.swift
<unknown>:0: error: index output filenames do not match input source files

error: [link] Building product 'App' failed
error: BuildError()

I'm getting the same error on Linux.