Keep _FORTIFY_SOURCE=2 for libvulkan when enabling _FORTIFY_SOURCE=3 globally

malloc_usable_size() is not allowed when _FORTIFY_SOURCE=3, so we keep
it 2 as a workaround.

Bug: b/291762537
Test: mm and presubmit
Change-Id: I2eb79bb9673aacfd36b0835edbf821059319189f

Author: ZijunZhaoCCK

vulkan/libvulkan/Android.bp

@@ -59,6 +59,11 @@ cc_library_shared {
         "-fstandalone-debug",
 
         //"-DLOG_NDEBUG=0",
+
+        // Keep -D_FORTIFY_SOURCE=2 in libvulkan.
+        // See b/291762537
+        "-U_FORTIFY_SOURCE",
+        "-D_FORTIFY_SOURCE=2",
     ],
 
     cppflags: [