[libcxx] Allow use of <atomic> in C++03. Try 3.

Summary:
After putting this question up on cfe-dev I have decided that it would be best to allow the use of `<atomic>` in C++03. Although static initialization is a concern the syntax required to get it is C++11 only. Meaning that C++11 constant static initialization cannot silently break in C++03, it will always cause a syntax error. Furthermore `ATOMIC_VAR_INIT` and `ATOMIC_FLAG_INIT` remain defined in C++03 even though they cannot be used because C++03 usages will cause better error messages.

The main change in this patch is to replace `__has_feature(cxx_atomic)`, which only returns true when C++ >= 11, to `__has_extension(c_atomic)` which returns true whenever clang supports the required atomic builtins.


This patch adds the following macros:
* `_LIBCPP_HAS_C_ATOMIC_IMP`      - Defined on clang versions which provide the C `_Atomic` keyword.
* `_LIBCPP_HAS_GCC_ATOMIC_IMP` - Defined on GCC > 4.7. We must use the fallback atomic implementation.
* `_LIBCPP_HAS_NO_ATOMIC_HEADER` - Defined when it is not safe to include `<atomic>`.

`_LIBCPP_HAS_C_ATOMIC_IMP` and `_LIBCPP_HAS_GCC_ATOMIC_IMP` are mutually exclusive, only one should be defined. If neither is defined then `<atomic>` is not implemented and including `<atomic>` will issue an error.

Reviewers: chandlerc, jroelofs, mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D11555

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@245463 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 20 deletions

diff --git a/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_and.pass.cpp b/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_and.pass.cpp
index 4c7c0432e..57355d304 100644
--- a/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_and.pass.cpp
+++ b/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_and.pass.cpp
@@ -23,10 +23,11 @@
 #include <type_traits>
 #include <cassert>
 
+#include "atomic_helpers.h"
+
 template <class T>
-void
-test()
-{
+struct TestFn {
+  void operator()() const {
     {
         typedef std::atomic<T> A;
         A t;
@@ -41,24 +42,10 @@ test()
         assert(std::atomic_fetch_and(&t, T(2)) == T(3));
         assert(t == T(2));
     }
-}
+  }
+};
 
 int main()
 {
-    test<char>();
-    test<signed char>();
-    test<unsigned char>();
-    test<short>();
-    test<unsigned short>();
-    test<int>();
-    test<unsigned int>();
-    test<long>();
-    test<unsigned long>();
-    test<long long>();
-    test<unsigned long long>();
-    test<wchar_t>();
-#ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
-    test<char16_t>();
-    test<char32_t>();
-#endif  // _LIBCPP_HAS_NO_UNICODE_CHARS
+    TestEachIntegralType<TestFn>()();
 }