[TEST-ONLY][swift][Caching] Fix some swift caching tests

Fix two problems from now enabled swift caching tests:
* Some destinations/requirements are not consistent across the test so
  the test can fail with certain test configuration.
* Make the test more reliable for different SDK configurations by
  abstracting out the number of module dependencies.

rdar://158600194

Author: cachemeifyoucan

Tests/SWBBuildSystemTests/SwiftCompilationCachingTests.swift

@@ -111,29 +111,29 @@ fileprivate struct SwiftCompilationCachingTests: CoreBasedTests {
                     numCompile += tasks.count
                 }
 
-                results.checkNote("0 hits / 4 cacheable tasks (0%)")
+                results.checkNote("0 hits / \(numCompile) cacheable tasks (0%)")
 
                 results.checkNoTask()
             }
             #expect(try readMetrics("one").contains("\"swiftCacheHits\":0,\"swiftCacheMisses\":\(numCompile)"))
 
             // touch a file, clean build folder, and rebuild.
             try await tester.fs.updateTimestamp(testWorkspace.sourceRoot.join("aProject/App.swift"))
-            try await tester.checkBuild(runDestination: .macOS, buildCommand: .cleanBuildFolder(style: .regular), body: { _ in })
+            try await tester.checkBuild(runDestination: .anyiOSDevice, buildCommand: .cleanBuildFolder(style: .regular), body: { _ in })
 
             tester.userInfo = rawUserInfo.withAdditionalEnvironment(environment: metricsEnv("two"))
             try await tester.checkBuild(runDestination: .anyiOSDevice, persistent: true) { results in
                 results.checkTask(.matchRule(["SwiftCompile", "normal", "arm64", "Compiling App.swift", "\(tmpDirPath.str)/Test/aProject/App.swift"])) { task in
                     results.checkKeyQueryCacheHit(task)
                 }
 
-                results.checkNote("4 hits / 4 cacheable tasks (100%)")
+                results.checkNote("\(numCompile) hits / \(numCompile) cacheable tasks (100%)")
             }
             #expect(try readMetrics("two").contains("\"swiftCacheHits\":\(numCompile),\"swiftCacheMisses\":0"))
         }
     }
 
-    @Test(.requireSDKs(.iOS))
+    @Test(.requireSDKs(.macOS))
     func swiftCachingSwiftPM() async throws {
         try await withTemporaryDirectory { tmpDirPath async throws -> Void in
             let commonBuildSettings = try await [