Add rpath to test runner binaries to find adjacent test dylib (swiftlang#9218)

Author: owenv

Sources/SwiftBuildSupport/PackagePIFProjectBuilder+Products.swift

@@ -1012,6 +1012,13 @@ extension PackagePIFProjectBuilder {
         // This should eventually be set universally for all package targets/products.
         settings[.LINKER_DRIVER] = "swiftc"
 
+        // A test-runner should always be adjacent to the dynamic library containing the tests,
+        // so add the appropriate rpaths.
+        settings[.LD_RUNPATH_SEARCH_PATHS] = [
+            "$(inherited)",
+            "$(RPATH_ORIGIN)"
+        ]
+
         let deploymentTargets = unitTestProduct.deploymentTargets
         settings[.MACOSX_DEPLOYMENT_TARGET] = deploymentTargets?[.macOS] ?? nil
         settings[.IPHONEOS_DEPLOYMENT_TARGET] = deploymentTargets?[.iOS] ?? nil

Tests/CommandsTests/TestCommandTests.swift

@@ -663,8 +663,7 @@ struct TestCommandTests {
                 }
             }
         } when: {
-            (buildSystem == .swiftbuild && .linux == ProcessInfo.hostOperatingSystem)
-                || ProcessInfo.hostOperatingSystem == .windows
+            ProcessInfo.hostOperatingSystem == .windows
         }
     }
 
@@ -1011,7 +1010,7 @@ struct TestCommandTests {
                 )
             }
         } when: {
-            buildSystem == .swiftbuild && ProcessInfo.hostOperatingSystem != .macOS
+            buildSystem == .swiftbuild && ProcessInfo.hostOperatingSystem == .windows
         }
     }