[libc++] XFAIL a test that does not behave properly on older Clang

rdar://53015486

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@366359 91177308-0d34-0410-b5e6-96231b3b80d8

test/libcxx/language.support/support.dynamic/libcpp_deallocate.sh.cpp

@@ -30,6 +30,10 @@
 // XFAIL: availability=macosx10.8
 // XFAIL: availability=macosx10.7
 
+// AppleClang < 10 incorrectly warns that aligned allocation is not supported
+// even when it is supported.
+// XFAIL: apple-clang-9
+
 // XFAIL: sanitizer-new-delete, ubsan
 
 // GCC doesn't support the aligned-allocation flags.