Unable to cross compiling against MUSL.

SwiftNIO SSH commit hash: e0ad5be6b474d24849b5b6ba8263bdfd0ede2eae

## Context:
Trying to compile `swift-nio-ssh` against MUSL getting the following errors.
```
/Users/zane/Downloads/swift-nio-ssh/Sources/NIOSSH/Keys And Signatures/NIOSSHCertifiedPublicKey.swift:740:17: error: cannot find 'timespec' in scope
738 | extension DispatchWallTime {
739 | init(secondsSinceEpoch: UInt64) {
740 | let t = timespec(tv_sec: time_t(secondsSinceEpoch), tv_nsec: 0)
| `- error: cannot find 'timespec' in scope
741 | self = DispatchWallTime(timespec: t)
742 | }

/Users/zane/Downloads/swift-nio-ssh/Sources/NIOSSH/Keys And Signatures/NIOSSHCertifiedPublicKey.swift:740:34: error: cannot find 'time_t' in scope
738 | extension DispatchWallTime {
739 | init(secondsSinceEpoch: UInt64) {
740 | let t = timespec(tv_sec: time_t(secondsSinceEpoch), tv_nsec: 0)
| `- error: cannot find 'time_t' in scope
741 | self = DispatchWallTime(timespec: t)
742 | }
```

## Steps to reproduce:
```
xcrun --toolchain swift swift build --swift-sdk aarch64-swift-linux-musl
# or
xcrun --toolchain swift swift build --swift-sdk x86_64-swift-linux-musl
```

## Environment
```sh
xcrun --toolchain swift swift --version
Apple Swift version 6.0.1 (swift-6.0.1-RELEASE)
Target: arm64-apple-macosx15.0

xcrun --toolchain swift swift sdk list
swift-6.0.1-RELEASE_static-linux-0.0.1
```
Operating system: 15.0 (24A335)

Start at Sources/NIOSSH/Keys And Signatures/NIOSSHCertifiedPublicKey.swift around line 740 and reproduce the failure with the listed swift build commands for the MUSL SDKs. Check the cross-compilation failure involving DispatchWallTime, timespec, and time_t; done means the project builds successfully for the affected MUSL targets.

Written by the indexing model from the issue text.