Remove unnecessary TSCLibc dependency (#4073)

Remove the `TSCLibc` dependency as we do not depend on any of the
interfaces from the module.  This matters particularly on Windows
where static linking Swift content is not available, so this will
reduce the amount of dirty memory due to the dynamic library link
that cannot be removed.

Author: compnerd

Sources/Commands/SwiftTool.swift

@@ -19,13 +19,17 @@ import PackageModel
 import SourceControl
 import SPMBuildCore
 import TSCBasic
-import TSCLibc
+
 import TSCUtility
 import Workspace
 import XCBuildSupport
 
 #if os(Windows)
 import WinSDK
+#elseif os(iOS) || os(macOS) || os(tvOS) || os(watchOS)
+import Darwin
+#else
+import Glibc
 #endif
 
 typealias Diagnostic = Basics.Diagnostic

Tests/FunctionalTests/MiscellaneousTests.swift

@@ -12,7 +12,7 @@ import PackageModel
 import SourceControl
 import SPMTestSupport
 import TSCBasic
-import TSCLibc
+
 import TSCUtility
 import Workspace
 import XCTest