Index: include/__config
===================================================================
--- include/__config
+++ include/__config
@@ -342,9 +342,11 @@
 #      endif
 #      if _LIBCPP_GLIBC_PREREQ(2, 17)
 #        define _LIBCPP_HAS_C11_FEATURES
+#        define _LIBCPP_HAS_TIMESPEC_GET
 #      endif
 #    else // defined(_LIBCPP_HAS_MUSL_LIBC)
 #      define _LIBCPP_HAS_QUICK_EXIT
+#      define _LIBCPP_HAS_TIMESPEC_GET
 #      define _LIBCPP_HAS_C11_FEATURES
 #    endif
 #  endif // __linux__
Index: include/cstdlib
===================================================================
--- include/cstdlib
+++ include/cstdlib
@@ -151,11 +151,11 @@
 using ::wctomb;
 using ::mbstowcs;
 using ::wcstombs;
-#ifdef _LIBCPP_HAS_QUICK_EXIT
+#if !defined(_LIBCPP_CXX03_LANG) && defined(_LIBCPP_HAS_QUICK_EXIT)
 using ::at_quick_exit;
 using ::quick_exit;
 #endif
-#ifdef _LIBCPP_HAS_C11_FEATURES
+#if _LIBCPP_STD_VER > 14 && defined(_LIBCPP_HAS_C11_FEATURES)
 using ::aligned_alloc;
 #endif
 
Index: include/ctime
===================================================================
--- include/ctime
+++ include/ctime
@@ -73,7 +73,7 @@
 using ::localtime;
 #endif
 using ::strftime;
-#if _LIBCPP_STD_VER > 14 && defined(_LIBCPP_HAS_C11_FEATURES)
+#if _LIBCPP_STD_VER > 14 && defined(_LIBCPP_HAS_TIMESPEC_GET)
 using ::timespec_get;
 #endif
 
Index: test/std/language.support/support.runtime/ctime.pass.cpp
===================================================================
--- test/std/language.support/support.runtime/ctime.pass.cpp
+++ test/std/language.support/support.runtime/ctime.pass.cpp
@@ -45,7 +45,7 @@
     static_assert((std::is_same<decltype(std::difftime(t,t)), double>::value), "");
     static_assert((std::is_same<decltype(std::mktime(&tm)), std::time_t>::value), "");
     static_assert((std::is_same<decltype(std::time(&t)), std::time_t>::value), "");
-#if TEST_STD_VER > 14 && defined(TEST_HAS_C11_FEATURES)
+#if TEST_STD_VER > 14 && defined(TEST_HAS_TIMESPEC_GET)
     static_assert((std::is_same<decltype(std::timespec_get(nullptr, 0)), int>::value), "");
 #endif
 #ifndef _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
Index: test/std/utilities/time/date.time/ctime.pass.cpp
===================================================================
--- test/std/utilities/time/date.time/ctime.pass.cpp
+++ test/std/utilities/time/date.time/ctime.pass.cpp
@@ -47,7 +47,7 @@
     static_assert((std::is_same<decltype(std::difftime(t,t)), double>::value), "");
     static_assert((std::is_same<decltype(std::mktime(&tm)), std::time_t>::value), "");
     static_assert((std::is_same<decltype(std::time(&t)), std::time_t>::value), "");
-#if TEST_STD_VER > 14 && defined(TEST_HAS_C11_FEATURES)
+#if TEST_STD_VER > 14 && defined(TEST_HAS_TIMESPEC_GET)
     static_assert((std::is_same<decltype(std::timespec_get(nullptr, 0)), int>::value), "");
 #endif
 #ifndef _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
Index: test/support/test_macros.h
===================================================================
--- test/support/test_macros.h
+++ test/support/test_macros.h
@@ -124,22 +124,29 @@
 
 // Sniff out to see if the underling C library has C11 features
 // Note that at this time (July 2018), MacOS X and iOS do NOT.
+// This is cribbed from __config; but lives here as well because we can't assume libc++
 #if __ISO_C_VISIBLE >= 2011 || TEST_STD_VER >= 11
 #  if defined(__FreeBSD__)
+//  Specifically, FreeBSD does NOT have timespec_get, even though they have all
+//  the rest of C11 - this is PR#38495
 #    define TEST_HAS_C11_FEATURES
 #  elif defined(__Fuchsia__)
 #    define TEST_HAS_C11_FEATURES
+#    define TEST_HAS_TIMESPEC_GET
 #  elif defined(__linux__)
 #    if !defined(_LIBCPP_HAS_MUSL_LIBC)
 #      if _LIBCPP_GLIBC_PREREQ(2, 17)
+#        define TEST_HAS_TIMESPEC_GET
 #        define TEST_HAS_C11_FEATURES
 #      endif
 #    else // defined(_LIBCPP_HAS_MUSL_LIBC)
 #      define TEST_HAS_C11_FEATURES
+#      define TEST_HAS_TIMESPEC_GET
 #    endif
 #  elif defined(_WIN32)
 #    if defined(_MSC_VER) && !defined(__MINGW32__)
 #      define TEST_HAS_C11_FEATURES // Using Microsoft's C Runtime library
+#      define TEST_HAS_TIMESPEC_GET
 #    endif
 #  endif
 #endif