[test] Disable parse_stdlib.sil on Apple platforms to unblock builders (#14098)

Tracked within Apple by <rdar://problem/36754225> Swift CI:
parse_stdlib.sil tests failing with vtable verification. The error is
an assertion failure that we haven't traced back to its cause yet:

    Assertion failed: (EntriesSZ == VTableEntryCache.size() && "Cache
    size is not equal to true number of VTable entries"), function
    verify, file /Users/buildnode/jenkins/workspace/
    oss-swift-package-osx/swift/lib/SIL/SILVerifier.cpp, line 4747.

Author: jrose-apple

validation-test/SIL/parse_stdlib.sil

@@ -3,3 +3,6 @@
 // RUN: %target-sil-opt -assume-parsing-unqualified-ownership-sil -enable-sil-verify-all=true %t.sil > /dev/null
 // REQUIRES: long_test
 // REQUIRES: nonexecutable_test
+
+// <rdar://problem/36754225> Swift CI: parse_stdlib.sil tests failing with vtable verification
+// XFAIL: objc_interop