Fix cross-compilation to the static Linux SDK

[leinelissen]

When cross-compiling a Vapor app with the Swift Static Linux SDK, postgres-nio will throw error: no such module 'Glibc'. This fix imports Musl instead of Glibc when it is available to fix cross-compilation.

Note: given other errors with the Static Linux SDK and Swift toolchain, you'll need to run at least the swift-6.0-DEVELOPMENT-SNAPSHOT-2024-09-17-a Swift development toolchain and corresponding Linux SDK. Also, there's an unreleased fix in swift-nio, so it's recommended to run at least the 1b33db2dea6a64d5b619b9e888175133c6d7f410 revision of the package when cross-compiling.

[0xTim]

Thanks!

@gwynne we really need to work static Linux SDK into the CI at some point

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.12%. Comparing base (9f84290) to head (8edd91b).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #510   +/-   ##
=======================================
  Coverage   55.12%   55.12%           
=======================================
  Files         127      127           
  Lines       10174    10174           
=======================================
  Hits         5608     5608           
  Misses       4566     4566           

Files with missing lines	Coverage Δ
...ources/ConnectionPoolModule/PoolStateMachine.swift	88.31% <ø> (ø)

... and 2 files with indirect coverage changes

[ffried]

Any chance this could make it into a release soon(-ish)? We're trying to enable multi-platform docker builds for our server side applications and this is one blocker (that can currently be worked around by manually adding postgres-nio as dependency with a fixed commit hash to the current HEAD of main).