Bump toolchain, use --enable-test-discovery (#130)

In the latest 5.3 toolchain all known issues with IndexStoreDB and SwiftPM support were resolved.

Resolves the second point of #42.

Thanks to this you no longer need to maintain `LinuxMain.swift` and `XCTestManifests.swift` files in your test suites, so these are deleted from the test app `Tests` directory.

Package.resolved

@@ -57,7 +57,7 @@
       },
       {
         "package": "swift-argument-parser",
-        "repositoryURL": "https://github.com/apple/swift-argument-parser",
+        "repositoryURL": "https://github.com/apple/swift-argument-parser.git",
         "state": {
           "branch": null,
           "revision": "92646c0cdbaca076c8d3d0207891785b3379cbff",

Package.swift

@@ -15,7 +15,7 @@ let package = Package(
   dependencies: [
     .package(url: "https://github.com/swift-server/async-http-client.git", from: "1.1.1"),
     .package(
-      url: "https://github.com/apple/swift-argument-parser",
+      url: "https://github.com/apple/swift-argument-parser.git",
       .upToNextMinor(from: "0.3.0")
     ),
     .package(

Sources/CartonHelpers/DefaultToolchain.swift

@@ -12,4 +12,4 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-public let defaultToolchainVersion = "wasm-5.3-SNAPSHOT-2020-10-13-a"
+public let defaultToolchainVersion = "wasm-5.3-SNAPSHOT-2020-10-15-a"

Sources/SwiftToolchain/Toolchain.swift

@@ -253,7 +253,7 @@ public final class Toolchain {
 
     let builderArguments = try [
       swiftPath.pathString, "build", "-c", isRelease ? "release" : "debug", "--build-tests",
-      "--destination", inferDestinationPath().pathString,
+      "--enable-test-discovery", "--destination", inferDestinationPath().pathString,
       "-Xswiftc", "-color-diagnostics",
     ]