[libc++][Android] XFAIL some tests for mblen/towctrans/wctrans (#116147)

These functions weren't added until API 26 (Android 8.0), but libc++ is
supported for API 21 and up.

These APIs are undeclared as of r.android.com/3216959.

Author: rprichard

libcxx/test/std/depr/depr.c.headers/stdlib_h.pass.cpp

@@ -8,6 +8,11 @@
 
 // test <stdlib.h>
 
+// mblen was added in Android API 26.
+// TODO: Switch from UNSUPPORTED to XFAIL once the Android CI Docker sysroot is
+// updated.
+// UNSUPPORTED: LIBCXX-ANDROID-FIXME && target={{.+}}-android{{(eabi)?(21|22|23|24|25)}}
+
 #include <stdlib.h>
 #include <cassert>
 #include <type_traits>

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

@@ -8,6 +8,11 @@
 
 // UNSUPPORTED: no-wide-characters
 
+// towctrans and wctrans were added in Android API 26.
+// TODO: Switch from UNSUPPORTED to XFAIL once the Android CI Docker sysroot is
+// updated.
+// UNSUPPORTED: LIBCXX-ANDROID-FIXME && target={{.+}}-android{{(eabi)?(21|22|23|24|25)}}
+
 // <wctype.h>
 
 #include <wctype.h>

libcxx/test/std/language.support/support.runtime/cstdlib.pass.cpp

@@ -8,6 +8,11 @@
 
 // test <cstdlib>
 
+// mblen was added in Android API 26.
+// TODO: Switch from UNSUPPORTED to XFAIL once the Android CI Docker sysroot is
+// updated.
+// UNSUPPORTED: LIBCXX-ANDROID-FIXME && target={{.+}}-android{{(eabi)?(21|22|23|24|25)}}
+
 #include <cstdlib>
 #include <cassert>
 #include <type_traits>

libcxx/test/std/strings/c.strings/cwctype.pass.cpp

@@ -10,6 +10,11 @@
 
 // UNSUPPORTED: no-wide-characters
 
+// towctrans and wctrans were added in Android API 26.
+// TODO: Switch from UNSUPPORTED to XFAIL once the Android CI Docker sysroot is
+// updated.
+// UNSUPPORTED: LIBCXX-ANDROID-FIXME && target={{.+}}-android{{(eabi)?(21|22|23|24|25)}}
+
 #include <cwctype>
 #include <type_traits>