Update driver for fully static Linux.

Sources/SwiftDriver/Jobs/GenericUnixToolchain+LinkerSupport.swift

@@ -18,7 +18,8 @@ import struct TSCBasic.AbsolutePath
 extension GenericUnixToolchain {
   private func defaultLinker(for targetTriple: Triple) -> String? {
     if targetTriple.os == .openbsd || targetTriple.os == .freeBSD ||
-        targetTriple.environment == .android {
+         targetTriple.environment == .android ||
+         targetTriple.isFullyStaticLinux {
       return "lld"
     }
 

Sources/SwiftDriver/Utilities/Triple+Platforms.swift

@@ -292,7 +292,21 @@ extension Triple {
       return conflatingDarwin ? "darwin" : darwinPlatform.platformName
 
     case .linux:
-      return environment == .android ? "android" : "linux"
+      switch environment {
+      case .musl:
+        // The triple for linux-static is <arch>-swift-linux-musl, to distinguish
+        // it from a "normal" musl set-up (ala Alpine).
+        if vendor == .swift {
+          return "linux-static"
+        }
+        fallthrough
+      case .musl, .musleabihf, .musleabi:
+        return "musl"
+      case .android:
+        return "android"
+      default:
+        return "linux"
+      }
     case .freeBSD:
       return "freebsd"
     case .openbsd:

Sources/SwiftDriver/Utilities/Triple.swift

@@ -1028,6 +1028,7 @@ extension Triple {
     case mesa
     case suse
     case openEmbedded = "oe"
+    case swift
 
     fileprivate static func parse(_ component: Substring) -> Triple.Vendor? {
       switch component {
@@ -1063,6 +1064,8 @@ extension Triple {
         return .suse
       case "oe":
         return .openEmbedded
+      case "swift":
+        return .swift
       default:
         return nil
       }
@@ -1706,13 +1709,21 @@ fileprivate extension Array {
   }
 }
 
-// MARK: - Linker support
+// MARK: - Fully static Linux support
 
 extension Triple {
-    /// Returns `true` if a given triple supports producing fully statically linked executables by providing `-static`
-    /// flag to the linker. This implies statically linking platform's libc, and of those that Swift supports currently
-    /// only Musl allows that reliably.
-    var supportsStaticExecutables: Bool {
-        self.environment == .musl
-    }
+  /// Returns `true` if this is the triple for Swift's fully statically
+  /// linked Linux target.
+  var isFullyStaticLinux: Bool {
+    self.vendor == .swift && self.environment == .musl
+  }
+
+  /// Returns `true` if a given triple supports producing fully
+  /// statically linked executables by providing `-static` flag to
+  /// the linker. This implies statically linking platform's libc,
+  /// and of those that Swift supports currently only Musl allows
+  /// that reliably.
+  var supportsStaticExecutables: Bool {
+    self.isFullyStaticLinux
+  }
 }