fix FreeBSD build

Summary:
Currently FreeBSD build is broken in master and possibly some previous releases due to unrecognized symbol `O_DIRECT`.
This PR will fix the build on FreeBSD
Closes https://github.com/facebook/rocksdb/pull/3560

Differential Revision: D7148646

Pulled By: miasantreble

fbshipit-source-id: 95b6c3d310fa531267c086b2cd40a5ab1c042b5a

env/env_test.cc

@@ -1143,7 +1143,7 @@ TEST_P(EnvPosixTestWithParam, Preallocation) {
     unique_ptr<WritableFile> srcfile;
     EnvOptions soptions;
     soptions.use_direct_reads = soptions.use_direct_writes = direct_io_;
-#if !defined(OS_MACOSX) && !defined(OS_WIN) && !defined(OS_SOLARIS) && !defined(OS_AIX) && !defined(OS_OPENBSD)
+#if !defined(OS_MACOSX) && !defined(OS_WIN) && !defined(OS_SOLARIS) && !defined(OS_AIX) && !defined(OS_OPENBSD) && !defined(OS_FREEBSD)
     if (soptions.use_direct_writes) {
       rocksdb::SyncPoint::GetInstance()->SetCallBack(
           "NewWritableFile:O_DIRECT", [&](void* arg) {
@@ -1205,7 +1205,7 @@ TEST_P(EnvPosixTestWithParam, ConsistentChildrenAttributes) {
       oss << test::TmpDir(env_) << "/testfile_" << i;
       const std::string path = oss.str();
       unique_ptr<WritableFile> file;
-#if !defined(OS_MACOSX) && !defined(OS_WIN) && !defined(OS_SOLARIS) && !defined(OS_AIX) && !defined(OS_OPENBSD)
+#if !defined(OS_MACOSX) && !defined(OS_WIN) && !defined(OS_SOLARIS) && !defined(OS_AIX) && !defined(OS_OPENBSD) && !defined(OS_FREEBSD)
       if (soptions.use_direct_writes) {
         rocksdb::SyncPoint::GetInstance()->SetCallBack(
             "NewWritableFile:O_DIRECT", [&](void* arg) {