Rework how we handle feature test macros

We do not want to conflict with the host standard library but also provide users with feature test macros

libcudacxx/.upstream-tests/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp

@@ -21,9 +21,9 @@
 TEST_NV_DIAG_SUPPRESS(cuda_demote_unsupported_floating_point)
 
 // NVRTC doesn't include host atomic making this feature test invalid
-// TODO: Should we define __cpp_lib_atomic_is_always_lock_free for NVRTC?
-#if !defined(__CUDACC_RTC__)
-#if !defined(__cpp_lib_atomic_is_always_lock_free)
+// TODO: Should we define __cccl_lib_atomic_is_always_lock_free for NVRTC?
+#if !defined(_LIBCUDACXX_COMPILER_NVRTC)
+#if !defined(__cccl_lib_atomic_is_always_lock_free)
 # error Feature test macro missing.
 #endif
 #endif

libcudacxx/.upstream-tests/test/std/utilities/meta/meta.const.eval/is_constant_evaluated.pass.cpp

@@ -17,14 +17,13 @@
 
 #include "test_macros.h"
 
-// libcudacxx does not have feature test macros... yet
-/*
-#ifndef __cpp_lib_is_constant_evaluated
+#if TEST_STD_VER > 17
+#ifndef __cccl_lib_is_constant_evaluated
 #if TEST_HAS_BUILTIN(__builtin_is_constant_evaluated)
-# error __cpp_lib_is_constant_evaluated should be defined
+# error __cccl_lib_is_constant_evaluated should be defined
 #endif
-#endif
-*/
+#endif // __cccl_lib_is_constant_evaluated
+#endif // TEST_STD_VER > 17
 
 template <bool> struct InTemplate {};
 

libcudacxx/.upstream-tests/test/std/utilities/meta/meta.unary/meta.unary.cat/is_integral.pass.cpp

@@ -88,7 +88,7 @@ int main(int, char**)
     test_is_integral<signed char>();
     test_is_integral<unsigned char>();
     test_is_integral<wchar_t>();
-#if defined(__cpp_lib_char8_t) && __cpp_lib_char8_t >= 201811L
+#if defined(__cccl_lib_char8_t) && __cccl_lib_char8_t >= 201811L
     test_is_integral<char8_t>();
 #endif