WIN32 support for path concatenation

Summary:
So far, Flipper has concatenated paths assuming is only ever built on unix-like systems.

For RNW, this approach fails.

This change is a very simple way of achieving WIN32 support without using any extra libraries or routines for path building.

Reviewed By: antonk52

Differential Revision: D39053479

fbshipit-source-id: e8b4b71cc1d17ca6aba88d40cad7d96a30ad1267

xplat/Flipper/ConnectionContextStore.cpp

@@ -125,7 +125,11 @@ void ConnectionContextStore::storeConnectionConfig(folly::dynamic& config) {
 }
 
 std::string ConnectionContextStore::absoluteFilePath(const char* filename) {
+#ifndef WIN32
   return std::string(deviceData_.privateAppDirectory + "/sonar/" + filename);
+#else
+  return std::string(deviceData_.privateAppDirectory + "\\sonar\\" + filename);
+#endif
 }
 
 std::string ConnectionContextStore::getCertificateDirectoryPath() {