Automerge: [ASan] [Windows] Fix a new test in mingw mode

The new test case added in 7817197
didn't work in mingw mode; defines set through `/D` only works when
using the clang-cl compiler driver, not the regular clang compiler
driver.

Switch this to use `-D`, which works with both plain clang and
clang-cl, so we don't need to use a lit macro for expanding
the right option to use.

Author: mstorsjo

compiler-rt/test/asan/TestCases/Windows/rtlsizeheap_zero.cpp

@@ -1,6 +1,6 @@
 // RUN: %clang_cl_asan %s %Fe%t
 // RUN: %env_asan_opts=windows_hook_rtl_allocators=true %run %t 2>&1 | FileCheck %s
-// RUN: %clang_cl_asan %s %Fe%t /DFAIL_CHECK
+// RUN: %clang_cl_asan %s %Fe%t -DFAIL_CHECK
 // RUN: %env_asan_opts=windows_hook_rtl_allocators=true not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-FAIL
 //
 // Verify that zero-size heap allocations report size 0 through Windows heap