Support compiling against Musl (#182)

Author: simonjbeaumont

Sources/ConcurrencyHelpers/Lock.swift

@@ -31,8 +31,10 @@ import Darwin
 #elseif os(Windows)
 import ucrt
 import WinSDK
-#else
+#elseif canImport(Glibc)
 import Glibc
+#elseif canImport(Musl)
+import Musl
 #endif
 
 #if os(Windows)

Sources/UnixSignals/UnixSignal.swift

@@ -16,6 +16,8 @@
 import Darwin
 #elseif canImport(Glibc)
 import Glibc
+#elseif canImport(Musl)
+import Musl
 #endif
 import Dispatch
 

Sources/UnixSignals/UnixSignalsSequence.swift

@@ -18,6 +18,9 @@ import Dispatch
 #elseif canImport(Glibc)
 @preconcurrency import Dispatch
 import Glibc
+#elseif canImport(Musl)
+@preconcurrency import Dispatch
+import Musl
 #endif
 import ConcurrencyHelpers
 

Tests/UnixSignalsTests/UnixSignalTests.swift

@@ -18,6 +18,8 @@ import XCTest
 import Darwin
 #elseif canImport(Glibc)
 import Glibc
+#elseif canImport(Musl)
+import Musl
 #endif
 
 final class UnixSignalTests: XCTestCase {