Use a better c++11 readiness check.

This is like https://codereview.chromium.org/443483002/ , but that check wasn't
as convincing as it could have been since clang accepts override and final as
an extension in c++98 mode. No intended behavior change.

If your bot can't deal with this, please let me know!

BUG=none
R=viettrungluu@chromium.org

Review URL: https://codereview.chromium.org/555383004

Cr-Commit-Position: refs/heads/master@{#295128}

base/macros.h

@@ -153,64 +153,8 @@ inline To implicit_cast(From const &f) {
 // containing the name of the variable.
 
 #undef COMPILE_ASSERT
-
-#if __cplusplus >= 201103L
-
-// Under C++11, just use static_assert.
 #define COMPILE_ASSERT(expr, msg) static_assert(expr, #msg)
 
-#else
-
-template <bool>
-struct CompileAssert {
-};
-
-#define COMPILE_ASSERT(expr, msg) \
-  typedef CompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1] ALLOW_UNUSED
-
-// Implementation details of COMPILE_ASSERT:
-//
-// - COMPILE_ASSERT works by defining an array type that has -1
-//   elements (and thus is invalid) when the expression is false.
-//
-// - The simpler definition
-//
-//     #define COMPILE_ASSERT(expr, msg) typedef char msg[(expr) ? 1 : -1]
-//
-//   does not work, as gcc supports variable-length arrays whose sizes
-//   are determined at run-time (this is gcc's extension and not part
-//   of the C++ standard).  As a result, gcc fails to reject the
-//   following code with the simple definition:
-//
-//     int foo;
-//     COMPILE_ASSERT(foo, msg); // not supposed to compile as foo is
-//                               // not a compile-time constant.
-//
-// - By using the type CompileAssert<(bool(expr))>, we ensures that
-//   expr is a compile-time constant.  (Template arguments must be
-//   determined at compile-time.)
-//
-// - The outer parentheses in CompileAssert<(bool(expr))> are necessary
-//   to work around a bug in gcc 3.4.4 and 4.0.1.  If we had written
-//
-//     CompileAssert<bool(expr)>
-//
-//   instead, these compilers will refuse to compile
-//
-//     COMPILE_ASSERT(5 > 0, some_message);
-//
-//   (They seem to think the ">" in "5 > 0" marks the end of the
-//   template argument list.)
-//
-// - The array size is (bool(expr) ? 1 : -1), instead of simply
-//
-//     ((expr) ? 1 : -1).
-//
-//   This is to avoid running into a bug in MS VC 7.1, which
-//   causes ((0.0) ? 1 : -1) to incorrectly evaluate to 1.
-
-#endif
-
 // bit_cast<Dest,Source> is a template function that implements the
 // equivalent of "*reinterpret_cast<Dest*>(&source)".  We need this in
 // very low-level functions like the protobuf library and fast math