Always define `FOLLY_USE_LIBCPP` to `0`/`1`

Summary:
Users may set `FOLLY_USE_LIBCPP` or `FOLLY_USE_LIBSTDCPP` to `0` or
`1`, so make sure everything checks it via `#if`.

Reviewed By: luciang

Differential Revision: D32496561

fbshipit-source-id: 5eee660b540af0bf1eaee4949576acf11c9be8d0

folly/Portability.h

@@ -220,7 +220,7 @@ constexpr bool kIsSanitize = false;
 // It turns out that GNU libstdc++ and LLVM libc++ differ on how they implement
 // the 'std' namespace; the latter uses inline namespaces. Wrap this decision
 // up in a macro to make forward-declarations easier.
-#ifdef FOLLY_USE_LIBCPP
+#if FOLLY_USE_LIBCPP
 #include <__config> // @manual
 #define FOLLY_NAMESPACE_STD_BEGIN _LIBCPP_BEGIN_NAMESPACE_STD
 #define FOLLY_NAMESPACE_STD_END _LIBCPP_END_NAMESPACE_STD

folly/concurrency/test/AtomicSharedPtrPerformance.cpp

@@ -18,7 +18,7 @@
 
 // AtomicSharedPtr-detail.h only works with libstdc++, so skip these tests for
 // other vendors
-#ifdef FOLLY_USE_LIBSTDCPP
+#if FOLLY_USE_LIBSTDCPP
 
 #include <folly/concurrency/AtomicSharedPtr.h>
 
@@ -236,10 +236,10 @@ int main(int, char**) {
   return 0;
 }
 
-#else // #ifdef FOLLY_USE_LIBSTDCPP
+#else // #if FOLLY_USE_LIBSTDCPP
 
 int main(int, char**) {
   return 1;
 }
 
-#endif // #ifdef FOLLY_USE_LIBSTDCPP
+#endif // #if FOLLY_USE_LIBSTDCPP

folly/concurrency/test/AtomicSharedPtrTest.cpp

@@ -18,7 +18,7 @@
 
 // AtomicSharedPtr-detail.h only works with libstdc++, so skip these tests for
 // other vendors
-#ifdef FOLLY_USE_LIBSTDCPP
+#if FOLLY_USE_LIBSTDCPP
 
 #include <folly/concurrency/test/AtomicSharedPtrCounted.h>
 
@@ -187,4 +187,4 @@ TEST(AtomicSharedPtr, DeterministicTest) {
     DSched::join(t);
   }
 }
-#endif // #ifdef FOLLY_USE_LIBSTDCPP
+#endif // #if FOLLY_USE_LIBSTDCPP

folly/concurrency/test/CoreCachedSharedPtrTest.cpp

@@ -18,7 +18,7 @@
 
 // AtomicSharedPtr-detail.h only works with libstdc++, so skip these tests for
 // other vendors
-#ifdef FOLLY_USE_LIBSTDCPP
+#if FOLLY_USE_LIBSTDCPP
 
 #include <atomic>
 #include <memory>
@@ -318,7 +318,7 @@ int main(int argc, char** argv) {
   return ret;
 }
 
-#endif // #ifdef FOLLY_USE_LIBSTDCPP
+#endif // #if FOLLY_USE_LIBSTDCPP
 
 #if 0
 // On Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz, 2 sockets, 28 cores, 56 threads.