[libcxx] Define _LIBCPP_HAS_C8RTOMB_MBRTOC8 to true if compiling with clang

libcxx/include/__config

@@ -1027,6 +1027,8 @@ typedef __char32_t char32_t;
 #    else
 #      define _LIBCPP_HAS_C8RTOMB_MBRTOC8 0
 #    endif
+#  elif defined(__clang__)
+#    define _LIBCPP_HAS_C8RTOMB_MBRTOC8 1
 #  else
 #    define _LIBCPP_HAS_C8RTOMB_MBRTOC8 0
 #  endif

libcxx/test/std/depr/depr.c.headers/uchar_h.compile.pass.cpp

@@ -11,6 +11,11 @@
 // Apple platforms don't provide <uchar.h> yet, so these tests fail.
 // XFAIL: target={{.+}}-apple-{{.+}}
 
+// The following platforms do not provide mbrtoc8 and c8rtomb so the tests fail
+// XFAIL: aix
+// XFAIL: freebsd
+// XFAIL: windows
+
 // mbrtoc16 not defined.
 // XFAIL: LIBCXX-PICOLIBC-FIXME
 

libcxx/test/std/strings/c.strings/cuchar.compile.pass.cpp

@@ -11,6 +11,11 @@
 // Apple platforms don't provide <uchar.h> yet, so these tests fail.
 // XFAIL: target={{.+}}-apple-{{.+}}
 
+// The following platforms do not provide mbrtoc8 and c8rtomb so the tests fail
+// XFAIL: aix
+// XFAIL: freebsd
+// XFAIL: windows
+
 // mbrtoc16 not defined.
 // XFAIL: LIBCXX-PICOLIBC-FIXME
 

libcxx/test/std/strings/c.strings/no_c8rtomb_mbrtoc8.verify.cpp

@@ -8,6 +8,13 @@
 
 // UNSUPPORTED: c++03
 
+// The following platforms do not provide mbrtoc8 and c8rtomb so the tests fail
+// XFAIL: aix
+// XFAIL: darwin
+// XFAIL: freebsd
+// XFAIL: windows
+// XFAIL: LIBCXX-PICOLIBC-FIXME
+
 #include <uchar.h>
 
 #include "test_macros.h"

libcxx/utils/libcxx/test/features.py

@@ -669,6 +669,7 @@ def _getLocaleFlagsAction(cfg, locale, alts, members):
             """,
         ),
     ),
+    Feature(name="aix", when=lambda cfg: "_AIX" in compilerMacros(cfg)),
 ]
 
 # Add features representing the build host platform name.