[NFC] Marking test added in r363975 as unsupported on Windows.

This test references a path that does not exist on Windows causing
it to emit different output from what was expected leading to a
failure when run on Windows.

llvm-svn: 364120

clang-tools-extra/test/clang-tidy/empty-database.cpp

@@ -1,3 +1,5 @@
+// UNSUPPORTED: system-windows
+
 // RUN: not clang-tidy -p %S/Inputs/empty-database %s 2>&1 | FileCheck %s
 
 // CHECK: LLVM ERROR: Cannot chdir into ""!