Fix boringSSL path when linking SDK from source.

Author: jonsimantov

CMakeLists.txt

@@ -198,8 +198,8 @@ if(DESKTOP)
 
   if(FIREBASE_USE_BORINGSSL)
     # Use BoringSSL instead of OpenSSL.
-    set(BORINGSSL_ROOT_DIR ${CMAKE_BINARY_DIR}/external/src/boringssl/src CACHE STRING "" FORCE)
-    set(BORINGSSL_BINARY_DIR ${CMAKE_BINARY_DIR}/external/src/boringssl-build CACHE STRING "" FORCE)
+    set(BORINGSSL_ROOT_DIR ${PROJECT_BINARY_DIR}/external/src/boringssl/src CACHE STRING "" FORCE)
+    set(BORINGSSL_BINARY_DIR ${PROJECT_BINARY_DIR}/external/src/boringssl-build CACHE STRING "" FORCE)
     set(OPENSSL_ROOT_DIR ${BORINGSSL_ROOT_DIR} CACHE STRING "" FORCE)
 
     # The call below to build_external_dependencies will make sure that these