Foundation: add ProcessInfo SPI for tests

Add the `_processPath` computed property on `ProcessInfo` to allow the
tests to access `_CFProcessPath`.  This removes the last CoreFoundation
API usage in the test suite, allowing it to build on Windows which does
not provide the CoreFoundation APIs to users.

Author: compnerd

Foundation/ProcessInfo.swift

@@ -192,3 +192,10 @@ open class ProcessInfo: NSObject {
         return NSFullUserName()
     }
 }
+
+// SPI for TestFoundation
+public extension ProcessInfo {
+  var _processPath: String {
+    return String(cString: _CFProcessPath())
+  }
+}

TestFoundation/TestBundle.swift

@@ -566,7 +566,7 @@ class TestBundle : XCTestCase {
         XCTAssertNotNil(maybeURL)
         guard let url = maybeURL else { return }
 
-        XCTAssertEqual(url.path, String(cString: _CFProcessPath()))
+        XCTAssertEqual(url.path, ProcessInfo.processInfo._processPath)
 #endif
     }
 }