Allow passing -nostdlib to clang linker driver

Embedded targets may need `-nostdlib` passed to `clang` linker driver in certain situations, see #1534 for more details.

Currently, `swiftc` doesn't recognize `-nostdlib` at all, while `-Xlinker -nostdlib` passed to a `swiftc` link job from the build system will be passed verbatim to the linker and not recognized by the linker driver. We should support this flag in `swiftc` to fix this.

Author: MaxDesiatov

Sources/SwiftOptions/Options.swift

@@ -608,6 +608,7 @@ extension Option {
   public static let driverScanDependenciesNonLib: Option = Option("-nonlib-dependency-scanner", .flag, attributes: [.helpHidden], helpText: "Use calls to `swift-frontend -scan-dependencies` instead of dedicated dependency scanning library")
   public static let nostartfiles: Option = Option("-nostartfiles", .flag, attributes: [.helpHidden, .frontend, .noInteractive, .doesNotAffectIncrementalBuild], helpText: "Do not link in the Swift language startup routines")
   public static let nostdimport: Option = Option("-nostdimport", .flag, attributes: [.frontend], helpText: "Don't search the standard library import path for modules")
+  public static let nostdlib: Option = Option("-nostdlib", .flag, attributes: [.helpHidden], helpText: "Don't link the C and compiler runtime libraries", group: .linkerOption)
   public static let numThreads: Option = Option("-num-threads", .separate, attributes: [.frontend, .doesNotAffectIncrementalBuild, .cacheInvariant], metaVar: "<n>", helpText: "Enable multi-threading and specify number of threads")
   public static let omitExtensionBlockSymbols: Option = Option("-omit-extension-block-symbols", .flag, attributes: [.helpHidden, .frontend, .noInteractive, .supplementaryOutput], helpText: "Directly associate members and conformances with the extended nominal when generating symbol graphs instead of emitting 'swift.extension' symbols for extensions to external types")
   public static let Onone: Option = Option("-Onone", .flag, attributes: [.frontend, .moduleInterface], helpText: "Compile without any optimization", group: .O)
@@ -1437,6 +1438,7 @@ extension Option {
       Option.driverScanDependenciesNonLib,
       Option.nostartfiles,
       Option.nostdimport,
+      Option.nostdlib,
       Option.numThreads,
       Option.omitExtensionBlockSymbols,
       Option.Onone,

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -6635,11 +6635,12 @@ final class SwiftDriverTests: XCTestCase {
 
     // Embedded Wasm link job
     do {
-      var driver = try Driver(args: ["swiftc", "-target", "wasm32-none-none-wasm", "test.o", "-enable-experimental-feature", "Embedded", "-wmo", "-o", "a.wasm"], env: env)
+      var driver = try Driver(args: ["swiftc", "-target", "wasm32-none-none-wasm", "test.o", "-enable-experimental-feature", "Embedded", "-wmo", "-nostdlib", "-o", "a.wasm"], env: env)
       let plannedJobs = try driver.planBuild()
       XCTAssertEqual(plannedJobs.count, 2)
       let _ /*autolinkJob*/ = plannedJobs[0]
       let linkJob = plannedJobs[1]
+      XCTAssertTrue(linkJob.commandLine.contains(.flag("-nostdlib")))
       XCTAssertFalse(linkJob.commandLine.contains(.flag("-force_load")))
       XCTAssertFalse(linkJob.commandLine.contains(.flag("-rpath")))
       XCTAssertFalse(linkJob.commandLine.contains(.flag("-lswiftCore")))
@@ -6648,19 +6649,19 @@ final class SwiftDriverTests: XCTestCase {
 
     do {
       let diags = DiagnosticsEngine()
-      var driver = try Driver(args: ["swiftc", "-target", "arm64-apple-macosx10.13",  "test.swift", "-enable-experimental-feature", "Embedded", "-parse-as-library", "-wmo", "-o", "a.out", "-module-name", "main", "-enable-library-evolution"], diagnosticsEngine: diags)
+      var driver = try Driver(args: ["swiftc", "-target", "arm64-apple-macosx10.13", "test.swift", "-enable-experimental-feature", "Embedded", "-parse-as-library", "-wmo", "-o", "a.out", "-module-name", "main", "-enable-library-evolution"], diagnosticsEngine: diags)
       _ = try driver.planBuild()
       XCTAssertTrue(diags.diagnostics.first!.message.text == Diagnostic.Message.error_no_library_evolution_embedded.text)
     } catch _ { }
     do {
       let diags = DiagnosticsEngine()
-      var driver = try Driver(args: ["swiftc", "-target", "arm64-apple-macosx10.13",  "test.swift", "-enable-experimental-feature", "Embedded", "-parse-as-library", "-o", "a.out", "-module-name", "main"], diagnosticsEngine: diags)
+      var driver = try Driver(args: ["swiftc", "-target", "arm64-apple-macosx10.13", "test.swift", "-enable-experimental-feature", "Embedded", "-parse-as-library", "-o", "a.out", "-module-name", "main"], diagnosticsEngine: diags)
       _ = try driver.planBuild()
       XCTAssertTrue(diags.diagnostics.first!.message.text == Diagnostic.Message.error_need_wmo_embedded.text)
     } catch _ { }
     do {
       let diags = DiagnosticsEngine()
-      var driver = try Driver(args: ["swiftc", "-target", "arm64-apple-macosx10.13",  "test.swift", "-enable-experimental-feature", "Embedded", "-parse-as-library", "-wmo", "-o", "a.out", "-module-name", "main", "-enable-objc-interop"], diagnosticsEngine: diags)
+      var driver = try Driver(args: ["swiftc", "-target", "arm64-apple-macosx10.13", "test.swift", "-enable-experimental-feature", "Embedded", "-parse-as-library", "-wmo", "-o", "a.out", "-module-name", "main", "-enable-objc-interop"], diagnosticsEngine: diags)
       _ = try driver.planBuild()
       XCTAssertTrue(diags.diagnostics.first!.message.text == Diagnostic.Message.error_no_objc_interop_embedded.text)
     } catch _ { }