Fix incorrect XFAIL

Author: ldionne

libcxxabi/test/uncaught_exception.pass.cpp

@@ -15,7 +15,7 @@
 // to undefined symbols when linking against a libc++ that re-exports the symbols,
 // but running against a libc++ that doesn't. Fortunately, usage of __cxa_uncaught_exception()
 // in the wild seems to be close to non-existent.
-// XFAIL: stdlib=apple-libc++ && target={{.+}}-apple-macosx10.{{9|10|11|12|13|14}}
+// XFAIL: stdlib=apple-libc++ && target={{.+}}-apple-macosx10.{{9|10|11|12|13|14|15}}
 // XFAIL: stdlib=apple-libc++ && target={{.+}}-apple-macosx{{11|12|13|14}}
 
 #include <cxxabi.h>