[libc++] Disable header deprecations until llvm#168041 is landed (llvm#169305)

The `#warning` causes diagnostics if system headers include deprecated
headers. llvm#168041 will add a way to deprecated headers properly, which
then also interacts nicely with system header suppression.

Author: philnik777

libcxx/include/__config

@@ -546,7 +546,10 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_DEPRECATED_(m)
 #  endif
 
-#  if defined(__DEPRECATED) && __DEPRECATED && !defined(_LIBCPP_DISABLE_DEPRECATION_WARNINGS)
+// FIXME: using `#warning` causes diagnostics from system headers which include deprecated headers. This can only be
+// enabled again once https://github.com/llvm/llvm-project/pull/168041 (or a similar feature) has landed, since that
+// allows suppression in system headers.
+#  if defined(__DEPRECATED) && __DEPRECATED && !defined(_LIBCPP_DISABLE_DEPRECATION_WARNINGS) && 0
 #    define _LIBCPP_DIAGNOSE_DEPRECATED_HEADERS 1
 #  else
 #    define _LIBCPP_DIAGNOSE_DEPRECATED_HEADERS 0

libcxx/test/std/depr/depr.cpp.headers/ccomplex.verify.cpp

@@ -14,6 +14,11 @@
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-modules-build
 
+// FIXME: using `#warning` causes diagnostics from system headers which include deprecated headers. This can only be
+// enabled again once https://github.com/llvm/llvm-project/pull/168041 (or a similar feature) has landed, since that
+// allows suppression in system headers.
+// XFAIL: *
+
 #include <ccomplex>
 
 // expected-warning@ccomplex:* {{<ccomplex> is deprecated in C++17 and removed in C++20. Include <complex> instead.}}

libcxx/test/std/depr/depr.cpp.headers/ciso646.verify.cpp

@@ -14,6 +14,11 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // UNSUPPORTED: clang-modules-build
 
+// FIXME: using `#warning` causes diagnostics from system headers which include deprecated headers. This can only be
+// enabled again once https://github.com/llvm/llvm-project/pull/168041 (or a similar feature) has landed, since that
+// allows suppression in system headers.
+// XFAIL: *
+
 #include <ciso646>
 
 // expected-warning@ciso646:* {{<ciso646> is removed in C++20. Include <version> instead.}}

libcxx/test/std/depr/depr.cpp.headers/cstdalign.verify.cpp

@@ -14,6 +14,11 @@
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-modules-build
 
+// FIXME: using `#warning` causes diagnostics from system headers which include deprecated headers. This can only be
+// enabled again once https://github.com/llvm/llvm-project/pull/168041 (or a similar feature) has landed, since that
+// allows suppression in system headers.
+// XFAIL: *
+
 #include <cstdalign>
 
 // expected-warning@cstdalign:* {{<cstdalign> is deprecated in C++17 and removed in C++20.}}

libcxx/test/std/depr/depr.cpp.headers/cstdbool.verify.cpp

@@ -14,6 +14,11 @@
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-modules-build
 
+// FIXME: using `#warning` causes diagnostics from system headers which include deprecated headers. This can only be
+// enabled again once https://github.com/llvm/llvm-project/pull/168041 (or a similar feature) has landed, since that
+// allows suppression in system headers.
+// XFAIL: *
+
 #include <cstdbool>
 
 // expected-warning@cstdbool:* {{<cstdbool> is deprecated in C++17 and removed in C++20.}}

libcxx/test/std/depr/depr.cpp.headers/ctgmath.verify.cpp

@@ -14,6 +14,11 @@
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: clang-modules-build
 
+// FIXME: using `#warning` causes diagnostics from system headers which include deprecated headers. This can only be
+// enabled again once https://github.com/llvm/llvm-project/pull/168041 (or a similar feature) has landed, since that
+// allows suppression in system headers.
+// XFAIL: *
+
 #include <ctgmath>
 
 // expected-warning@ctgmath:* {{<ctgmath> is deprecated in C++17 and removed in C++20. Include <cmath> and <complex> instead.}}