Fixup compilation failures for some compilers

Author: milseman

Sources/System/Internals/Exports.swift

@@ -160,8 +160,8 @@ internal func setTLS(_ key: _PlatformTLSKey, _ p: UnsafeMutableRawPointer?) {
 }
 internal func getTLS(_ key: _PlatformTLSKey) -> UnsafeMutableRawPointer? {
   #if os(Windows)
-  FlsGetValue(key)
+  return FlsGetValue(key)
   #else
-  pthread_getspecific(key)
+  return pthread_getspecific(key)
   #endif
 }

Sources/System/Internals/Mocking.swift

@@ -191,9 +191,16 @@ internal func _mockOffT(
 // Force paths to be treated as Windows syntactically if `enabled` is
 // true.
 internal func _withWindowsPaths(enabled: Bool, _ body: () -> ()) {
-  guard enabled else { return body() }
+  #if ENABLE_MOCKING
+  guard enabled else {
+    body()
+    return
+  }
   MockingDriver.withMockingEnabled { driver in
     driver.forceWindowsSyntaxForPaths = true
     body()
   }
+  #else
+  body()
+  #endif
 }