diff --git a/libcxx/include/__chrono/duration.h b/libcxx/include/__chrono/duration.h
--- a/libcxx/include/__chrono/duration.h
+++ b/libcxx/include/__chrono/duration.h
@@ -534,6 +534,9 @@
   inline namespace chrono_literals
   {
 
+    _LIBCPP_DIAGNOSTIC_PUSH
+    _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wliteral-suffix")
+    _LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wliteral-suffix")
     constexpr chrono::hours operator""h(unsigned long long __h)
     {
         return chrono::hours(static_cast<chrono::hours::rep>(__h));
@@ -598,6 +601,7 @@
     {
         return chrono::duration<long double, nano> (__ns);
     }
+    _LIBCPP_DIAGNOSTIC_POP
 
 } // namespace chrono_literals
 } // namespace literals
diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -4452,6 +4452,9 @@
 {
   inline namespace string_literals
   {
+    _LIBCPP_DIAGNOSTIC_PUSH
+    _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wliteral-suffix")
+    _LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wliteral-suffix")
     inline _LIBCPP_INLINE_VISIBILITY
     basic_string<char> operator "" s( const char *__str, size_t __len )
     {
@@ -4485,6 +4488,7 @@
     {
         return basic_string<char32_t> (__str, __len);
     }
+    _LIBCPP_DIAGNOSTIC_POP
   } // namespace string_literals
 } // namespace literals
 #endif
diff --git a/libcxx/include/string_view b/libcxx/include/string_view
--- a/libcxx/include/string_view
+++ b/libcxx/include/string_view
@@ -914,6 +914,9 @@
 {
   inline namespace string_view_literals
   {
+    _LIBCPP_DIAGNOSTIC_PUSH
+    _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wliteral-suffix")
+    _LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wliteral-suffix")
     inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
     basic_string_view<char> operator "" sv(const char *__str, size_t __len) _NOEXCEPT
     {
@@ -947,6 +950,7 @@
     {
         return basic_string_view<char32_t> (__str, __len);
     }
+    _LIBCPP_DIAGNOSTIC_POP
   } // namespace string_view_literals
 } // namespace literals
 #endif
diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
--- a/libcxx/utils/libcxx/test/features.py
+++ b/libcxx/utils/libcxx/test/features.py
@@ -103,8 +103,7 @@
   Feature(name=lambda cfg: 'apple-clang-{__clang_major__}.{__clang_minor__}'.format(**compilerMacros(cfg)),                        when=_isAppleClang),
   Feature(name=lambda cfg: 'apple-clang-{__clang_major__}.{__clang_minor__}.{__clang_patchlevel__}'.format(**compilerMacros(cfg)), when=_isAppleClang),
 
-  Feature(name='clang',                                                                                                            when=_isClang,
-          actions=[AddCompileFlag('-D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER')]),
+  Feature(name='clang',                                                                                                            when=_isClang),
   Feature(name=lambda cfg: 'clang-{__clang_major__}'.format(**compilerMacros(cfg)),                                                when=_isClang),
   Feature(name=lambda cfg: 'clang-{__clang_major__}.{__clang_minor__}'.format(**compilerMacros(cfg)),                              when=_isClang),
   Feature(name=lambda cfg: 'clang-{__clang_major__}.{__clang_minor__}.{__clang_patchlevel__}'.format(**compilerMacros(cfg)),       when=_isClang),
diff --git a/libcxx/utils/libcxx/test/params.py b/libcxx/utils/libcxx/test/params.py
--- a/libcxx/utils/libcxx/test/params.py
+++ b/libcxx/utils/libcxx/test/params.py
@@ -117,9 +117,10 @@
 
   Parameter(name='enable_warnings', choices=[True, False], type=bool, default=True,
             help="Whether to enable warnings when compiling the test suite.",
-            actions=lambda warnings: [] if not warnings else [
-              AddOptionalWarningFlag(w) for w in _warningFlags
-            ]),
+            actions=lambda warnings: [] if not warnings else
+              [AddOptionalWarningFlag(w) for w in _warningFlags] +
+              [AddCompileFlag('-D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER')]
+            ),
 
   Parameter(name='debug_level', choices=['', '0', '1'], type=str, default='',
             help="The debugging level to enable in the test suite.",