Reland "Turn libbase into a component"

src/base/platform/semaphore.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_BASE_PLATFORM_SEMAPHORE_H_
 #define V8_BASE_PLATFORM_SEMAPHORE_H_
 
+#include "src/base/base-export.h"
 #include "src/base/lazy-instance.h"
 #if V8_OS_WIN
 #include "src/base/win32-headers.h"
 #endif
 
 #if V8_OS_MACOSX
 #include <mach/semaphore.h>  // NOLINT
 #elif V8_OS_POSIX
 #include <semaphore.h>  // NOLINT
 #endif
 
 namespace v8 {
 namespace base {
 
 // Forward declarations.
 class TimeDelta;
 
 // ----------------------------------------------------------------------------
 // Semaphore
 //
 // A semaphore object is a synchronization object that maintains a count. The
 // count is decremented each time a thread completes a wait for the semaphore
 // object and incremented each time a thread signals the semaphore. When the
 // count reaches zero,  threads waiting for the semaphore blocks until the
 // count becomes non-zero.
 
-class Semaphore final {
+class V8_BASE_EXPORT Semaphore final {
  public:
   explicit Semaphore(int count);
   ~Semaphore();
 
   // Increments the semaphore counter.
   void Signal();
 
   // Decrements the semaphore counter if it is positive, or blocks until it
   // becomes positive and then decrements the counter.
   void Wait();
@@ skipping 47 matching lines @@
   typedef typename LazyDynamicInstance<Semaphore, CreateSemaphoreTrait<N>,
                                        ThreadSafeInitOnceTrait>::type type;
 };
 
 #define LAZY_SEMAPHORE_INITIALIZER LAZY_DYNAMIC_INSTANCE_INITIALIZER
 
 }  // namespace base
 }  // namespace v8
 
 #endif  // V8_BASE_PLATFORM_SEMAPHORE_H_