Try to fix Android build.

llvm-svn: 295769
diff --git a/llvm/lib/Support/Unix/Path.inc b/llvm/lib/Support/Unix/Path.inc
index 94cb681..b0aab16 100644
--- a/llvm/lib/Support/Unix/Path.inc
+++ b/llvm/lib/Support/Unix/Path.inc
@@ -346,7 +346,9 @@
 
 static bool is_local_impl(struct STATVFS &Vfs) {
 #if defined(__linux__)
-  constexpr uint32_t CIFS_MAGIC_NUMBER = 0xFF534D42;
+#ifndef CIFS_MAGIC_NUMBER
+#define CIFS_MAGIC_NUMBER 0xFF534D42
+#endif
   switch ((uint32_t)Vfs.f_type) {
   case NFS_SUPER_MAGIC:
   case SMB_SUPER_MAGIC: