[libc++] Remove redundant conditionals for Apple platforms

[ldionne]

Summary

In a bunch of places, we used to check whether LIBCXX_BUILDING_LIBCXXABI
is defined OR we're building for an Apple platform. This used to
be necessary in a time when Apple's build script did NOT define
LIBCXX_BUILDING_LIBCXXABI. However this is not relevant anymore
since Apple's build does define LIBCXX_BUILDING_LIBCXXABI.

[ldionne]

I'll try this out and back out if it breaks something -- I tested locally but we never know.

libcxx/src/exception.cpp

 //===------------------------ exception.cpp -------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "exception"
 #include "new"
 #include "typeinfo"
 
-#if defined(LIBCXXRT) || defined(LIBCXX_BUILDING_LIBCXXABI) || \
-  (defined(__APPLE__) && !defined(_LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY))
+#if defined(LIBCXXRT) || defined(LIBCXX_BUILDING_LIBCXXABI)
   #include <cxxabi.h>
   using namespace __cxxabiv1;
   #define HAVE_DEPENDENT_EH_ABI 1
 #endif
 
 #if defined(_LIBCPP_ABI_MICROSOFT)
 #include "support/runtime/exception_msvc.ipp"
 #include "support/runtime/exception_pointer_msvc.ipp"

libcxx/src/support/runtime/stdexcept_default.ipp

 //===--------------------- stdexcept_default.ipp --------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "../../include/refstring.h"
 
 /* For _LIBCPPABI_VERSION */
 #if !defined(_LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY) &&                           \
-    (defined(LIBCXX_BUILDING_LIBCXXABI) || defined(__APPLE__) ||               \
-     defined(LIBCXXRT))
+    (defined(LIBCXX_BUILDING_LIBCXXABI) || defined(LIBCXXRT))
 #include <cxxabi.h>
 #endif
 
 static_assert(sizeof(std::__libcpp_refstring) == sizeof(const char*), "");
 
 namespace std // purposefully not using versioning namespace
 {
 

libcxx/src/typeinfo.cpp

 #if defined(_WIN64)
   value ^= value >> 32;
 #endif
 
   return value;
 }
 #endif // _LIBCPP_ABI_MICROSOFT
 
-// FIXME: Remove __APPLE__ default here once buildit is gone.
 // FIXME: Remove the _LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY configuration.
-#if (!defined(LIBCXX_BUILDING_LIBCXXABI) && !defined(LIBCXXRT) &&              \
-     !defined(__GLIBCXX__) && !defined(__APPLE__) &&                           \
-     !defined(_LIBCPP_ABI_VCRUNTIME)) ||   \
+#if (!defined(LIBCXX_BUILDING_LIBCXXABI) &&               \
+     !defined(LIBCXXRT) &&                                \
+     !defined(__GLIBCXX__) &&                             \
+     !defined(_LIBCPP_ABI_VCRUNTIME)) ||                  \
     defined(_LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY)
 std::type_info::~type_info()
 {
 }
 #endif