Adjust XFAIL for over_max_size test

Author: ldionne

libcxx/test/std/strings/basic.string/string.capacity/over_max_size.pass.cpp

@@ -8,6 +8,14 @@
 
 // UNSUPPORTED: no-exceptions
 
+// This test fails when using a built library that does not contain
+// 15860446a8c3, which changed the return value of max_size(). Without
+// that change, the built library believes the max size to be one greater
+// than it really is, and we fail to throw `length_error` from `string::resize()`,
+// which is explicitly instantiated in the built library.
+//
+// XFAIL: using-built-library-before-llvm-21
+
 // <string>
 
 // size_type max_size() const; // constexpr since C++20

libcxx/utils/libcxx/test/features.py

@@ -733,10 +733,24 @@ def check_gdb(cfg):
 # Helpers to define correspondances between LLVM versions and vendor system versions.
 # Those are used for backdeployment features below, do not use directly in tests.
 DEFAULT_FEATURES += [
+    Feature(
+        name="_target-has-llvm-22",
+        when=lambda cfg: BooleanExpression.evaluate(
+            "TBD",
+            cfg.available_features,
+        ),
+    ),
+    Feature(
+        name="_target-has-llvm-21",
+        when=lambda cfg: BooleanExpression.evaluate(
+            "TBD",
+            cfg.available_features,
+        ),
+    ),
     Feature(
         name="_target-has-llvm-20",
         when=lambda cfg: BooleanExpression.evaluate(
-            "_target-has-llvm-21 || target={{.+}}-apple-macosx26.{{\d+(.\d+)?}}",
+            "_target-has-llvm-21 || target={{.+}}-apple-macosx{{26.[0-9](.\d+)?}}",
             cfg.available_features,
         ),
     ),
@@ -835,7 +849,7 @@ def check_gdb(cfg):
 # a libc++ flavor that enables availability markup. Similarly, a test could fail when
 # run against the system library of an older version of FreeBSD, even though FreeBSD
 # doesn't provide availability markup at the time of writing this.
-for version in ("12", "13", "14", "15", "16", "17", "18", "19", "20"):
+for version in ("12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22"):
     DEFAULT_FEATURES.append(
         Feature(
             name="using-built-library-before-llvm-{}".format(version),