Fix Windows strcmp for Unicode (facebook#8190)

Summary:
The code for strcmp that was present does work when compiled for Windows unicode file paths.

Needs backporting to:
* 6.17.fb
* 6.18.fb
* 6.19.fb

Pull Request resolved: facebook#8190

Reviewed By: akankshamahajan15

Differential Revision: D27765588

Pulled By: jay-zhuang

fbshipit-source-id: 89f8a5ac61fd7edc758340dfd335b0a5f96dae6e

port/win/env_win.cc

@@ -682,7 +682,8 @@ IOStatus WinFileSystem::GetChildren(const std::string& dir,
     // which appear only on some platforms
     const bool ignore =
         ((data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) != 0) &&
-        (strcmp(data.cFileName, ".") == 0 || strcmp(data.cFileName, "..") == 0);
+        (RX_FNCMP(data.cFileName, ".") == 0 ||
+         RX_FNCMP(data.cFileName, "..") == 0);
     if (!ignore) {
       auto x = RX_FILESTRING(data.cFileName, RX_FNLEN(data.cFileName));
       result->push_back(FN_TO_RX(x));

port/win/port_win.h

@@ -355,6 +355,7 @@ extern void SetCpuPriority(ThreadId id, CpuPriority priority);
 #define RX_FILESTRING std::wstring
 #define RX_FN(a) ROCKSDB_NAMESPACE::port::utf8_to_utf16(a)
 #define FN_TO_RX(a) ROCKSDB_NAMESPACE::port::utf16_to_utf8(a)
+#define RX_FNCMP(a, b) ::wcscmp(a, RX_FN(b).c_str())
 #define RX_FNLEN(a) ::wcslen(a)
 
 #define RX_DeleteFile DeleteFileW
@@ -379,6 +380,7 @@ extern void SetCpuPriority(ThreadId id, CpuPriority priority);
 #define RX_FILESTRING std::string
 #define RX_FN(a) a
 #define FN_TO_RX(a) a
+#define RX_FNCMP(a, b) strcmp(a, b)
 #define RX_FNLEN(a) strlen(a)
 
 #define RX_DeleteFile DeleteFileA